A rogue cell tower spotter. Browsers can't read your SIM, but they
can watch the shape of your mobile connection — and a fake tower
(an IMSI catcher) leaves fingerprints. Add the cells your phone
sees and Towerwatch scores each one for suspicion.
Everything runs in your browser. Nothing is uploaded, ever.
🔍 What a web page can & can't see
Can see
Connection type — 2g / 3g / 4g class, speed and
latency estimates via the Network Information API (Chrome, Edge, Android).
Sudden changes — a drop from 4G to 2G, or the connection dying
and returning, is the loudest IMSI-catcher tell there is.
Your position — with permission, so sightings can be pinned
to a place and compared over time.
Can't see
Cell ID, LAC/TAC, MCC/MNC — no browser API exposes the radio
layer. Those come from the phone's own field-test screen or a netmonitor app.
Signal strength in dBm — same reason.
Neighbour cell lists — Android and iOS keep these private to the OS.
So Towerwatch does both halves: it watches live what
the browser is allowed to know, and lets you feed in the cell details from
a netmonitor app (NetMonster, Cellular-Z, CellMapper, or Android's
*#*#4636#*#* menu). The heuristics do the rest.
How to get your cell data (30 seconds)
Install a free netmonitor app — NetMonster or Cellular-Z on Android.
Note the serving cell: MCC, MNC, LAC/TAC,
CID, radio type (GSM/UMTS/LTE/NR) and signal in dBm.
Type it into Log a cell below, or export CSV/JSON from the app and drop
the file in. Repeat whenever you move, or when something feels off.
📶 Live connection watch
Network class—
Downlink—
Round trip—
Position—
Idle — press Start watching to
begin logging connection changes.
Event timeline
No events yet.
🗒️ Log a cell
⚖️ Verdict
No cells logged yet — add one above, or press
Load demo data to see how a caught IMSI catcher looks.
🌍 Cross-check against OpenCelliD optional
A cell that no public database has ever seen is the single strongest sign of a
fake tower. Towerwatch can ask OpenCelliD whether each logged cell is known. It needs a free
API token, which is kept in this browser only and is sent to opencellid.org and nowhere else.
Some browsers block the request (no CORS headers) — if so it fails quietly and every other
heuristic still works.
🧭 If Towerwatch flags something
Don't panic. Dead spots, rural 2G fallback and temporary "cells on
wheels" at festivals or building sites all look suspicious and are entirely innocent.
Repeat the measurement. A real rogue tower follows you or sits in one
place; noise doesn't reproduce.
Compare with a second phone on another operator, standing beside you.
Turn off 2G in your phone's network settings — most catchers need that
downgrade to work.
Report it to your operator or national telecom regulator using the
export button, timestamps and coordinates included.