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Indoor mobile signal: the best networks for coverage inside buildings

House and mobile phone mast icons

The retailers featured on this page may compensate us when our readers follow links to their websites and make a purchase. More

We show you how to find mobile networks in your area that have good reception inside buildings, plus explain why indoor blackspots happen. SIM Sherpa is your trusty guide. Last updated: April 29th 2020

Causes of indoor blackspots

Why you might have bad mobile signal indoors

A brick wall

Building materials get in the way

Mobile phone signal behaves very similarly to radio waves (and even a bit like sound). And we're all familiar with your car radio dropping out when you go through a tunnel.

It's no different with mobile signal. It works best when it can get to your phone with as few disruptions as possible, although it can still bounce around a bit. If you're indoors, it's got to get through walls.

If you think about sound, you have high, medium and low pitches, also known as frequencies. Lower pitches or frequencies get through building materials better. It's why it's always the bass from music you can hear.

The same principle is true when it comes to mobile phone signal, as we explain in the next section.

Some networks use better frequencies for indoor coverage

Frequencies on a radio dial

Different frequencies like radio stations

We have four actual mobile networks in the UK (EE, Vodafone, O2 and Three). And then there's loads of other providers that use that four for signal.

Just like radio stations, they can't all broadcast on the same channels, on the same frequencies, because they'd clash. So they've historically used different ones. And this has an effect on signal.

So they split out the various types of mobile signal onto different frequencies. There's GSM, 2G and 3G used for calls and texts. And 3G, 4G and 5G that are used for varying speeds of data.

The way they're split out means some networks are broadcasting calls and texts on better frequencies for getting indoors and others have 4G data that's better at getting inside.

Why there’s not simply one best network for coverage inside

EE logoO2 logoThree logoVodafone logo

We'd love to say with certainty which is best

Like the example of hearing the bass of someone's TV through your walls, the best chance that call signal has of getting into your home is by being on a low fequency.

Out of the UK's networks, O2 and Vodafone both send their 2G/3G call signal on a low 900 MHz frequency, while EE and Three’s are higher at 1800 Mhz and 2100 Mhz. And the lower the better.

As a generalisation you could say Vodafone and O2 have better indoor signal for calls. But it's not a 100% cut and dry thing. Imagine the TV was turned up louder, you'd hear more details, even the higher frequencies.

So if one network has a transmitter closer to your house than another, it might still give you better coverage inside than a further away one on a lower frequency.

And every mobile network also now deploys other technology to improve their reception inside buildings, like 4G calling and WiFi calling, which give them extra ways to keep your phone connected.

Useful link: Solutions to poor indoor mobile signal

What can you do?

You can test out some networks before committing

A selection of pay as you go SIM cards

You can test each network for free

If you're willing to put in a little effort, the best way to find the best network to join permanently is to test each one out in real life. And there are ways you can do this for free.

Each of the big four mobile networks has a free pay as you go SIM card that you can order online (see the links below). As long as your phone's unlocked, you can test them in there one by one.

You don't even have to top the SIM up. From our most recent check, each SIM allows you to at least ring the top up line without credit. Or you can have someone ring you on the number provided.

Do this with WiFi calling and 4G calling turned off on your phone and you'll be able to hear how well the calls work. If it works well, you know you're safe to join them or a provider that uses them on pay monthly.

Order a free test SIM for each network now

Click a network logo to order a free pay as you go SIM

EE logo
O2 logo
Three logo
Vodafone logo

Or you can test a network during your returns period

BT's 30 day network guarantee

BT even give you 30 days to trial themSee their SIMs

at BT.com
(opens in new window)

If the method above sounds to long-winded for you or you already suspect one network might be better indoors for you, then you do have the option of ordering a pay monthly deal without testing it first.

British consumer rights mean that if you order your product online, you've got 14 days to change your mind and the network has to let you leave without settling the entire contract. BT even give you 30 days on SIM only.

It means you could order a pay monthly SIM (or even phone if you don't unbox it), test everything's in order as quick as possible, and return if you're not happy (phones need to be in an unused condition).

The main risk here is that you forget to cancel or use the phone and the network don't accept your return. Otherwise, it's a foolproof way to test for certain what the provider is like.

We can help you find a cheap pay monthly SIM only or phone deal using the links below.

Useful link: Compare SIM only deals | Compare phone contracts

You can also predict indoor coverage without a test SIM

Screenshot of Ofcom's indoor signal check

Not all the info provided is completeUse Ofcom's tool

at ofcom.org.uk
(opens in new window)

We understand both the approaches above might seem a little too much risk or effort up front. So there are some online resources you can use to give you some pointers without physically testing a SIM card.

Each network now predicts their own indoor coverage on their network maps here. And the government regulator Ofcom have an indoor signal checking tool too for each.

You could get a cheaper deal with a virtual operator that uses one of the main networks to bring their customers signal. Here's who each provider uses:

EE

BT Mobile, Virgin Mobile, Asda Mobile, Plusnet Mobile (you may see masts marked as Orange and T-Mobile on mastdata.com).

O2

giffgaff, Tesco Mobile and Sky Mobile.

Three

iD Mobile, SMARTY, Superdrug Mobile (see may see masts labelled as Hutchinson on mastdata.com.

Vodafone

Lebara, Talkmobile and VOXI.

Ofcom's tool is alright. There's a fair amount of missing data in there though. If you want to go really technical, you can use mastdata.com's database to find your nearest masts. It's a paid service but they offer free trials.

Combine all the coverage checkers available and ordering test pay as you go SIMs and you'll get a good picture of what networks are viable options for you to get a decent signal indoors.

Useful link: All about ordering test SIM cards

4G calling can improve your indoor mobile coverage

Three's 4G calling service banner

Three use low-frequency 4G to get insideHow 4G calling works

at three.co.uk
(opens in new window)

As we've explained above in our section about the causes of indoor blackspots, it's lower frequency signal that's best at getting through building materials and inside.

It tends to be the case that if a network's 2G and 3G signal (used mainly for calls and texts) is on less-optimal higher frequencies, their 4G will be on lower ones. But 4G was originally designed only to carry data.

Most modern phones now have a feature called 4G calling (VoLTE). This allows your phone to use 4G for calls too, as long as your mobile network supports it (and not all of them do).

4G calling means there's more available frequencies for your phone to tap into for calls, especially for networks like EE and Three, whose regular calls are on high frequencies but whose 4G tends to be on lower ones.

Networks with 4G calling: BT Mobile, EE, iD Mobile, O2, Sky Mobile, Three, Vodafone

WiFi calling can help if your network and phone supports it

Vodafone explanation of WiFi calling

Some schemes support more phonesSee our rankings

here at simsherpa.com
(opens in new window)

If your building is somewhere that mobile signal struggles to get inside but is somewhere that has WiFi, then WiFi calling could be another option for solving lack of calls due to indoor blackspots.

In a nutshell, WiFi calling lets your phone connect into a mobile network via a WiFi connection, rather than conventional mobile signal. You can make and take calls in the normal way on your regular number.

It's similar to 4G calling, in that only certain mobile networks support it and you'll need a phone that has the feature. We recommend checking in advance with a network that your model is supported, as it varies a lot.

In many ways WiFi calling is even more useful than 4G calling, because it can work in places where even the best mobile signal has zero chance of getting to, like on the London Underground.

It certainly beats the faff and expense of buying an old-school mobile signal booster.

Networks with WiFi calling: BT Mobile, EE, iD Mobile, O2, Sky Mobile, Three, Vodafone

Mobile signal repeaters have fallen out of favour recently

Vodafone signal booster

Vodafone sell their own signal boostersHow it works

at vodafone.co.uk
(opens in new window)

There was a time a few years ago when the only available cure for bad indoor mobile signal was to get a signal booster, a box that uses your home WiFi to create a mini 3G transmitter in your house.

It was only ever the main networks that offered these and you often had to complain or beg them to give you one. You might even have to pay for one (which we find a little unfair).

If your phone and network support WiFi calling, a signal booster is unnecessary. But Vodafone do still sell a signal booster called Sure Signal for a one-off cost if you don't have that option.

To be honest, we think it's only really worth going down the route of getting one if you've tried everything else on this page and still come up with no joy.

Useful link: Latest pricing for Vodafone's Sure Signal

How each network performs

Indoor coverage on each mobile network compared

Click on a logo to skip to particular providers or read the whole section

Three logo
BT Mobile logo
EE logo
giffgaff logo
ID logo
O2 logo
SMARTY logo
Talkmobile logo
Virgin Mobile logo
Vodafone logo
VOXI logo

Three's extra network technology helps out with indoor calls

Three's network map

Three use VoLTE to make calls over 4G tooSee network map

at three.co.uk
(opens in new window)

Looking at what frequencies each network carries their 3G calling signal on, Three are at a slight disadvantage broadcasting on a higher 2100 MHz frequency, which will make harder work getting through walls.

That's not to say there's no chance. The nearer you are to a 3G mast, the better it'll be able to get through. See Three's network map here and Ofcom/Mastdata to check the strength of their 3G calls signal where you go.

To work around any difficulty of their 3G getting indoors, Three have been one of the leaders in VoLTE (4G calling). Their 4G Supervoice uses their low frequency 4G signal to get into buildings (read Three's instructions here to make sure your phone will work with it).

On top of that, they also have the most flexible WiFi Calling scheme called InTouch. This uses WiFi signal to make and take calls and even supports regular SMS text messages too (read more here).

If you're not confident, there's always the option to order a free Three pay as you go SIM that will let you test. Or if you want to go straight for a contract, Three offer the same 14-day returns policy every network must.

Useful link: Three's SIM only deals | Three's phone contracts

BT Mobile indoor coverage is helped by 4G- and WiFi calling

BT Mobile coverage checker

Check 4G, 3G 2G at your addressCheck BT coverage

at BT.com
(opens in new window)

On the face of it BT Mobile don't use ideal frequencies for getting the 2G/3G for phone signal into buildings, 1800 MHz and 2100 MHz (EE's network). Lower than this would be more favourable.

If you have a phone that isn't supported by WiFi calling or 4G calling (check the "Is my phone compatible?" FAQs here and here), there's a lower chance of decent indoor signal but we wouldn't write it off completely.

You still have the option to check local masts and predicted coverage using Ofcom and mastdata.com methods above (also use BT's network map to check if you're near 2G and 3G masts).

There's no option to get a free pay as you go test SIM from BT Mobile (although their pay monthly SIMs do let you try them for 30 days and return if you're not happy).

Useful link: Our full BT Mobile review

EE have extra network features to boost calls indoors

EE coverage map

See what masts are in your areaUse EE network map

at EE.co.uk
(opens in new window)

The most conclusive way to test EE's indoor mobile signal is just to order one of their free pay as you go SIMs. Put it in your phone and get someone to call you where you want to test (4G calling won't work though).

EE actually use some of the less suitable frequencies for regular indoor call signal (1800 MHz and 2100 MHz). But if you have the right phone, and join on a pay monthly plan, you'll get access to 4G calling and WiFi calling.

As some of EE's 4G is broadcast on lower 800 MHz, having 4G calling should give you a better shot at strong signal inside. Check your phone is supported by EE here in their help section.

It's worth using EE's network map and/or the resources from Ofcom and mastdata.com to check what types of masts EE have in your local area, and their proximity to your building.

Useful link: EE's 14-day returns policy

giffgaff use naturally-better frequencies for indoor calls

giffgaff's coverage checker

Make sure you're near masts they useCheck giffgaff's map

at giffgaff.com
(opens in new window)

Using the O2 network gives giffgaff a natural advantage with indoor reception for phone calls, because the 2G and 3G signal it uses for calls is mostly on a low 900 MHz frequency (sometimes 2100 MHz though).

As we say in our section on the causes of indoor blackspots, the lower frequency, the better it generally is at penetrating through building walls.

It's important to make sure you're in a good area for 2G/3G coverage on giffgaff (use their network map here to confirm), because they don't have 4G calling or WiFi calling to help out, even though O2 do.

You can order a free SIM card from giffgaff to test but you'll need to top up in order to activate it (you can get £5 free credit with a £10 top up here). For a truly free way to test see O2's PAYG SIMs.

Useful link: giffgaff SIM only plans | giffgaff phone contracts

iD Mobile's extra network features help with signal inside

iD Mobile's coverage checker

See how strong 3G call signal is near youUse iD's signal checker

at idmobile.co.uk
(opens in new window)

The Three network that iD Mobile uses doesn't naturally run on the ideal frequencies for having the best chance of decent signal for calls indoors (their 3G is on high frequencies).

That needn't be a problem if you live close enough to a Three antenna anyway (check via this page at idmobile.co.uk). But if it is, then iD Mobile have other solutions that can help.

iD are one of the few low-cost (virtual) operators to offer both 4G calling and WiFi calling. This helps because lots of their 4G is broadcast on the indoor blackspot busting 800 MHz frequency.

As with other networks iD's WiFi calling and 4G calling is subject to your phone being supported (see their guide here). iD don't have free test SIMs to order but you can get one from Three directly without paying.

Useful link: iD Mobile's 14-day returns policy

O2 have good frequencies for calls inside and extra features

O2's indoor coverage checker

O2 will predict your indoor coverageCheck your O2 signal

at O2.co.uk
(opens in new window)

As long as you take a pay monthly deal, O2 are one of the best equipped mobile networks to be able to make and take phone calls inside (some of the extra features don't work on pay as you go plans though).

To start, the 2G and 3G signal that carries regular calls on O2 is mostly on a nice low 900 MHz frequency, giving it a good shot of getting through walls into buildings, without the need for extra technology.

But if that does struggle to get in, it's backed up by 4G calling and WiFi calling options on pay monthly plans. As with all other providers, you'll need a phone with the right software installed on it, and O2 are little more restrictive than others (see their guide here).

You're also in the position to order a free test pay as you go SIM card from O2. But bear in mind this will only test if calls work via 2G and 3G indoors, because neither WiFi calling nor 4G calling work on O2's PAYG.

Useful link: See what masts O2 have in your area

Plusnet Mobile have no extras to help with indoor calls

Plusnet's 4G/3G/2G map

Only 2G/3G carries calls on Plusnet MobileCheck 2G/3G signal

at Plus.net
(opens in new window)

Using EE's network is an advantage for Plusnet Mobile customers in terms of the amount of UK landmass with good outdoor 4G coverage but the high frequencies used to carry phone calls aren't optimal for getting inside.

And unlike EE and BT Mobile (who use EE), Plusnet don't give their customers the extra features 4G Calling and WiFi that could get round any indoor coverage problems, if they exist.

That doesn't mean you should discount them entirely, because if the buildings where you want signal are near a 2G/3G transmitter, there's a decent chance of call signal getting in (see Plusnet's network map).

Ultimately, we'd recommend doing a real life test if you're unsure. Plusnet don't do a free pay as you go SIM, so you could order a free one from EE, do a test and then go back and order from Plusnet.

Or you can take advantage of Plusnet's 14-day returns policy and cancel a SIM you take from them if you find it doesn't work to your satisfactions (you may still have to pay for usage in that period).

Useful link: Plusnet 12-month SIMs | Plusnet 30-day SIMs

Sky Mobile use better frequencies to get call signal inside

Sky Mobile indoor coverage map

See signal strength near youCheck Sky coverage

at Sky.com
(opens in new window)

If you didn't know, Sky Mobile uses the O2 network for signal, which we've already explained above lends itself better to getting into buildings because 2G/3G phone calls are mostly on low 900 MHz frequencies.

Like O2, Sky also have 4G calling technology on all their plans. But you'll need to make sure your phone is supported here. It means there's much better chance of call signal being good inside your home.

Sky have a WiFi calling facility too. The list of supported phones isn't huge, and you'll need to have bought your handset from Sky to guarantee it'll work (see their help section here).

Sky Mobile also provide a prediction of your indoor coverage on their network map here, which we'd recommend checking in advance. Mastdata will show you where nearby O2 transmitters are too.

There's no free PAYG SIM on Sky to use for a proper test (you could get a free one from O2 directly and come back to Sky). If you're confident, you could order a contract and cancel within 14 days if you're not satisfied.

Useful link: Sky SIM only plans | Sky phone contracts

SMARTY's frequencies aren't optimal for signal in buildings

SMARTY's coverage checker

You'll need good 3G signal for callsCheck 3G signal

at SMARTY.co.uk
(opens in new window)

On the face of it, the higher 2100 MHz frequency that SMARTY uses on the Three network for carrying phone calls via 3G has a lower chance of getting indoors than other providers.

It doesn't mean they're a complete write-off. If the buildings you want signal in are near enough their 3G transmitters, it's still got a healthy shot at getting inside to let you make calls.

Use SMARTY's coverage checker here to find out their 3G signal strength where you want to use your phone. And use Ofcom and Mastdata's maps to check proximity to your nearest antenna.

Failing that, you could do a robust test by ordering a free pay as you go SIM card from Three themselves (you have to pay up front on SMARTY) and ensure 4G and WiFi are turned off when you do your test.

Useful link: SMARTY's SIM only plans

Talkmobile: no extra technology but good frequencies

Talkmobile coverage map

They predict indoor coverageCheck their signal

at Talkmobile.co.uk
(opens in new window)

As Talkmobile use the Vodafone network, their 2G/3G that carries calls and texts is broadcast on a nice low 900 MHz frequencies, giving it a decent chance of getting inside on its own.

And it needs to because Talkmobile don't have any of the extra technology, WiFi calling and 4G calling, to help it out. It's one of a few differences between joining Talkmobile and Vodafone directly.

There's no free pay as you go SIM card on Talkmobile any more that you could order to do a test. But they do offer 1-month plans and you're covered by the same 14-day returns you get with any other provider.

Useful link: Talkmobile's SIM only plans

Tesco Mobile's 2G/3G use good frequencies for indoor signal

Tesco Mobile coverage checker

Results for indoor and outdoor coverageUse coverage checker

at tescomobile.com
(opens in new window)

Using O2's network is an advantage for Tesco Mobile because the 2G/3G signals that calls are carried on are on low-range 900 MHz frequencies that should do a better job of penetrating buildings.

That's a good job, because Tesco don't currently support extra network features that boost your indoor coverage like 4G calling or WiFi calling (O2 have this if you join them directly on pay monthly).

As with all networks, if you want to check in advance before committing to their official coverage checker here predicts your indoor signal strength. And Ofcom and Mastdata's maps are useful too for an independent view.

You can also order a free pay as you go SIM card from Tesco too for testing. Or utilise the fact that you can cancel a contract within 14-days if you're not satisfied anyway (check full returns policy here first).

Useful link: Tesco SIM only contracts | Tesco phone contracts

Virgin Mobile now have extra to help call signal inside

Virgin Mobile network map

Look for strong 2G and 3G signal for callsCheck your local signal

at virginmedia.com
(opens in new window)

Using EE's network is excellent for 4G download speeds on Virgin Mobile but it does mean the 2G/3G signal used for calls is on 1800 MHz and 2100 MHz, which generally is less-suitable for getting through walls etc.

And Virgin differ from EE and BT Mobile (who use EE's network), because they don't offer 4G calling as a backup if that 2G/3G signal can't get through (calls don't work on 4G). But they do now have some WiFi calling.

If you're close enough to EE's 2G/3G transmitters the lack of 4G calling won't necessarily be a problem (Virgin's coverage checker here predicts signal strength in each postcode). You can use Ofcom/Mastdata too.

If you want to test out Virgin Mobile's coverage for real, they don't have any free pay as you go SIMs any more. The only way is to order a pay monthly SIM and return it within the 14-day period if it's no good.

Useful link: Virgin Mobile 14-day returns policy

Vodafone use low frequencies and have 4G/WiFi calling too

Vodafone's coverage map

See signal strength where you areSee network map

at vodafone.co.uk
(opens in new window)

Alongside O2, Vodafone are one of the networks with the most amount of tools at their disposal to get you good mobile signal for making calls where you're indoors.

This is thanks to a combination of their calls being transmitted over nice-low 900 MHz on 2G and 3G, which has a better chance of getting through walls and other building materials than higher frequencies.

Additionally, if you join on a pay monthly SIM only or phone contract (not Vodafone Basics), you'll also benefit from Vodafone's 4G calling and WiFi technology too (make sure your phone is supported up front though).

The combination of all the above should make Vodafone one of the better choices for indoor coverage. Check you're in a strong area for their signal using their map here. And remember you can order a free test SIM too.

Or you can order a phone contract or SIM only deal from Vodafone and take advantage of their 30-day Network Satisfaction Guarantee, which lets you cancel your contract within 30 days if you're unhappy with their network.

Useful link: Vodafone SIM only | Vodafone phone contracts

VOXI uses naturally good frequencies for indoor coverage

VOXI's network map

Look for specifically at 2G/3G signal for callsCheck local signal

at VOXI.co.uk
(opens in new window)

As explained in the section about Vodafone, using the low 900 MHz frequencies for 2G/3G phone call carrying signal is a good thing for getting inside. VOXI use Vodafone's network, so you get that same advantage.

Where VOXI have a disadvantage over their parent is that they don't yet offer WiFi calling or 4G calling. These make good backups if the regular signal doesn't penetrate into your building.

You can't order a VOXI SIM card to test without actually paying for a plan first. So if you want to test what your experience would be like for free, order a Vodafone PAYG SIM and turn off WiFi and 4G calling.

You can also try and predict VOXI's indoor coverage where you are by using their network map here and checking 2G and 3G strength near your building. Or look at Vodafone's results on Ofcom and Mastdata's maps.

Useful link: Our full VOXI network review

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