Will cellular backup work inside your building?

What weakens signal indoors

• Metal roofs and metal siding. Warehouses, shops and many newer commercial buildings block a lot of signal.
• Concrete, brick and stone, especially thick walls and floors.
• Low-E and tinted glass. The coating that keeps heat out also blocks cellular signal, so a window isn't always the answer.
• Basements and interior rooms with no outside walls.
• Metal shelving, server racks and equipment near the router.
• Distance from the tower. At the edge of a carrier's coverage, every wall matters more.

Test at the spot where the router will sit

1. Pick the spot first: where the main internet comes in, or where the router can reach it with a network cable.
2. Borrow phones on Verizon, AT&T and T-Mobile. Staff phones are usually enough to cover all three.
3. Stand at that spot and open each phone's signal readout. On an iPhone, dial *3001#12345#* to open Field Test. On Android, look under Settings, About phone, SIM status.
4. Write down the signal strength (often shown as RSRP) for each carrier, then run a speed test on each one.
5. Try a second spot nearer an outside wall or higher up, and compare.

Reading the numbers

Signal strength is shown in negative numbers, and closer to zero is better. As a rough guide for LTE, around -80 dBm is strong, around -100 dBm is weak but usually usable, and below about -110 dBm is poor. Bars on the screen are less useful because every phone draws them differently.

A router with good antennas usually does a little better than a phone in the same spot, so a carrier that works on a phone will work on the router. If every carrier is poor at every spot you tried, plan for an external antenna before you order.

Where to put the router

• High is better than low. On a shelf beats on the floor.
• An outside wall or a window facing the nearest tower beats an interior room.
• Keep it away from metal racks, refrigerators and other large equipment.
• Put it on a battery backup with the main modem, since many outages come with a power problem.

When you need an external antenna

If the building blocks signal, an external antenna fixes it more reliably than moving the router around. The antenna mounts outside on a wall or the roof, and a cable runs to the router inside. It matters most in metal buildings, basements and rural sites far from a tower.

The router needs connectors for one. The Peplink MAX BR1 Pro 5G has them. If you're using your own router, check its specifications for antenna connectors before you rely on an antenna.

What we do before you order

Send us your address and, if you tested, the readings you got. We'll recommend the carrier that's strongest there and tell you whether an antenna is worth planning for. FAILOVER5 plans run on Verizon, AT&T or T-Mobile from $88 a month, month to month, so if a carrier turns out to be weak inside your building, you can switch.

Backup internet for

• Warehouses and distribution
• Auto repair shops
• Retail stores