Short answer
Carrier and FCC coverage maps are computer predictions of outdoor service, so they cannot tell you how a particular house does inside. Check on site instead: on each carrier you might use, read the signal outside and in every room that matters, at more than one time of day. A signal app with GPS turns that walk-through into a map, and the free Cell Surveys app can also show the average signal other users recorded nearby in the last 30 days.
By Eli TrevinoUpdated
Coverage Maps Are Predictions
Every carrier publishes a coverage map, and every one of them is a model, not a measurement. AT&T calls its map "a predicted high-level approximation of wireless coverage." Verizon's map "shows approximate outdoor coverage and is not a guarantee of service." T-Mobile's "approximates anticipated coverage outdoors."
The FCC's National Broadband Map is built the same way: the carriers generate its mobile coverage areas with propagation models, for a phone outdoors or in a moving vehicle, and it says it does not cover service indoors. It is still worth a look, because it puts every carrier on the same terms at one address, and it also lists the home internet providers there.
None of these maps knows what the house is made of. Walls, roofs, and energy-efficient windows can cost more signal than the distance to the tower, which is why signal is so often worse inside than out.
What to Check at the House
| Check | How | Why it matters |
|---|---|---|
| Signal outside | Read it at the curb and in the yard | Tells you whether the network reaches the street at all, before the walls take their share |
| Every room you will use | Bedrooms, office, kitchen, and any basement | Interior rooms and rooms behind energy-efficient windows can lose most of the outdoor signal |
| Upper and lower floors | Same spot on each floor | Upper floors usually do better; basements and ground floors behind other buildings do worst |
| Each carrier you might use | Your phone, plus a friend's or a family member's on another network | One network can be solid in a house while another is unusable |
| More than one time of day | A weekday evening as well as a weekend afternoon | Evenings are when networks are busiest, so data can slow even where signal looks fine |
| The backup plan | The home internet providers listed for the address | Good home internet makes Wi-Fi calling a reliable fallback in weak rooms |
Use the number, not the bars. Here is how to read your signal in dBm: for LTE and 5G, better than −90 dBm is good and below −110 dBm is effectively no service. iPhones do not let apps show that number, so on an iPhone it means Apple's hidden Field Test Mode; here is why, and how to open it.
Apartments and Rentals
The unit matters more than the building. A corner unit on an upper floor facing the nearest tower can have good service while an interior unit two floors down has none. Test in the unit you would actually rent, not the model unit or the lobby, and ask current tenants which carrier they use and how it holds up.
Map the house instead of noting it down. The free Cell Surveys app for iPhone and Android records your signal with GPS as you walk, and every spot lands on its heatmap as a colored square. Before you visit, turn on Everyone's coverage in Settings to see the average signal other app users recorded around the address in the last 30 days, in squares about 110 meters across. It combines all carriers and only covers places where people using the app have been, so treat it as a first look. With Cell Surveys Pro, parcel boundaries and county property details are on the map, standing on the property locks the app to its parcel, and the Parcel dashboard maps the readings on a 5-meter grid.
If the Signal Is Weak
A weak result is not automatically a dealbreaker. If the house has good home internet, Wi-Fi calling covers calls and texts. If the signal outside is usable but the walls block it, a carrier network extender or a booster may fix it; if it is weak outside too, only a different carrier will. Our guide to weak signal at home walks through the fixes, cheapest first.
