How to check whether there is enough mobile signal at your house

Where the number is, on your own phone

• Android. Settings → About phone → Status, or SIM status. Look for 'Signal strength': you will see something like −103 dBm. On some models it sits under Settings → Connections.
• iPhone. Field Test Mode opens by dialling *3001#12345#* and pressing call. A service screen opens with the cell measurements; look for RSRP. To leave, close the app.
• Either of them. Note the reading in three places: where there is never any signal, next to the window, and outside the house. The difference between those three numbers is your problem, measured.

What the number means

It is a power and it runs negative, so the less negative, the better: −80 is far better than −110. On 4G the measurement that matters is called RSRP, and the range the standard itself contemplates runs from −44 dBm (right beside the mast) to −140 dBm (nothing). That range is defined in 3GPP TS 36.133; what follows, by contrast, is our own working rule and not a standard:

• Better than −85 dBm — signal to spare. If you have this outside and nothing inside, your case is a textbook one and it turns out very well.
• Between −85 and −100 — good or normal signal. This is the range a booster works comfortably in.
• Between −100 and −110 — tight. It can be done, and this is where putting the antenna in the right place rather than the convenient one shows most.
• Worse than −110 — on the edge. Sometimes height and a well-aimed directional antenna get it out, and sometimes not. It is exactly the case where you measure before selling anything.
• No reading, or −140 — there is nothing to amplify on that band.

A warning about the reading: a single instant's number is worth nothing. Stand still for half a minute and watch how it moves. A reading that jumps twelve points up and down while you stand still is a bounced signal, and a bounced signal is worse than a weak steady one.