How to improve indoor mobile signal

Why indoor signal is always worse than outdoor

Mobile signals are radio waves. Every material they pass through absorbs some of their energy — a process called attenuation. A brick wall can reduce signal strength by 10 dB; a concrete slab up to 20 dB. Given that each 10 dB drop halves the perceived signal strength, a modern well-insulated building can absorb nearly all usable signal before it reaches you.

The frequency band your network uses also matters. High-frequency signals (like mid-band 5G at 3.5 GHz) carry more data but penetrate walls poorly. Low-frequency signals (like 700 MHz 4G or low-band 5G) travel further and pass through buildings more easily — which is why Ofcom measures indoor and outdoor coverage separately, and why the two scores can differ dramatically.

1. Turn on Wi-Fi calling first

Wi-Fi calling routes voice calls and texts over your broadband connection rather than the mobile network. If you have a reasonable broadband connection at home, enabling it costs nothing and solves the problem instantly for calls and SMS. All four UK MNOs support it — EE, O2, Vodafone and Three — as do most major MVNOs.

On iPhone: Settings → Phone → Wi-Fi Calling. On Android: Phone app → Settings → Calls → Wi-Fi Calling. Your handset must support it and your SIM must be active on a plan that includes it (almost all do).

2. Check your coverage data — it might be your network, not your building

Before spending money on any solution, check whether a different network would perform better indoors at your address. Ofcom collects indoor signal predictions for every UK postcode, and CheckCoverage surfaces that data alongside outdoor scores. If EE scores 40% indoors at your postcode and O2 scores 90%, the simplest fix is a SIM swap.

Check your postcode's indoor scores →

3. Move closer to a window or go upstairs

Signal enters a building through windows far more easily than through walls. If you're making a call, moving to the window nearest to the direction of the closest mast can improve signal by one or two bars. Upper floors typically have a better line of sight to masts than ground floors, though basements are almost always the worst spot.

4. Use a femtocell (operator-provided)

A femtocell is a small box provided by your network that creates a personal mini-mast in your home, using your broadband to backhaul the signal. O2 offers the Sure Signal device; EE and Vodafone have similar products. They're free or cheap for eligible customers with documented poor indoor coverage. The downside: they only work for customers on that specific network.

5. Consider an Ofcom-approved signal booster

Passive boosters — window-mounted film and cables — are legal and safe but provide modest gains (3–6 dB). Active boosters that amplify signal are tightly regulated: only single-operator devices approved by Ofcom are legal in the UK. Most cheap repeaters sold on marketplaces are illegal because they amplify across multiple bands and can interfere with emergency services. If in doubt, contact your network directly — they can advise on approved options.

6. Check when your network's 5G uses low-band spectrum

EE and Three have deployed significant low-band 5G at 700 MHz. Because this frequency penetrates walls almost as well as traditional 4G, customers with a 5G handset on those networks may find their indoor 5G signal is actually stronger than their indoor 4G was. If your phone shows 5G outdoors but drops to 4G inside, check your handset's 5G settings — some devices deprioritise low-band 5G unless explicitly configured.

7. Talk to your landlord or building manager

If you're in a new-build or a commercial property, the building may have a Distributed Antenna System (DAS) installed — an internal antenna network. Many new large developments include one. If yours doesn't, and signal is a building-wide problem, a collective approach to the landlord or management company is often more effective than individual solutions.

Frequently asked questions