Signal strength is how strong the radio signal from a mobile tower is at your device. It's most precisely measured in dBm (decibel-milliwatts), a negative number where closer to zero means stronger.
What the numbers mean
- -70 dBm or better: Excellent — full bars, fast data
- -85 to -70 dBm: Good — 4-5 bars, usable speed
- -100 to -85 dBm: Fair — 2-3 bars, slower
- -110 to -100 dBm: Weak — 1 bar, calls only
- Below -110 dBm: Effectively no signal
How to check your dBm
- iPhone: dial
*3001#12345#*for Field Test Mode - Android: Settings → About Phone → SIM Status → Signal Strength
The bars/dots on your status bar are a rough abstraction over the actual dBm reading — and different phones map them differently.
Why it matters
On a multi-network plan like Fuse, your phone reads dBm from all available networks and picks the strongest. On a single-network plan, you're stuck with whatever that one network is delivering.