WavelensWhat your phone can detect, what an ESP32 adds, and what only an SDR will hear
People ask which companion they need. Often the answer is none: a phone already hears the signals most people care about. This page lays out what each piece of hardware can physically receive, so the choice is about radio, not marketing.
The phone: Bluetooth LE and Wi-Fi
An Android phone has a Bluetooth radio and a Wi-Fi radio, both at 2.4 GHz (Wi-Fi also at 5 GHz), and an app can listen to what they receive. That covers a lot: item trackers, wearables, drones broadcasting Remote ID, body cams and dash cams with a Bluetooth or Wi-Fi link, plate-reader units with a setup hotspot, video doorbells, and fleet telematics boxes.
Its limits are Android's, not the radio's. Apps get Wi-Fi scan results only every 30 to 40 seconds, and only from the channels the phone chooses to visit. Long-range Bluetooth (LE Coded PHY) and Wi-Fi Aware depend on the phone model. And the antenna is tiny and wherever the phone happens to be lying, often behind your body or inside a steel car.
An ESP32 (Spotter): the same bands, heard better
An ESP32 is a small Wi-Fi and Bluetooth board. It does not add new frequencies. What it adds is listening time and an antenna: it can sit on one Wi-Fi channel and hear every beacon on it, scan Bluetooth continuously, and use an external antenna placed against the glass. In practice a short-lived hotspot the phone misses between scans, or hears only at the kerb, the ESP32 hears a block earlier. What Spotter hears, in detail.
An RTL-SDR (Scanner): the rest of the spectrum
A software-defined radio is a receiver whose tuning is done in software. The common RTL-SDR dongles cover roughly 24 MHz to 1.7 GHz, which is where a different set of things live: tyre-pressure sensors, key fobs and weather stations (315 and 433 MHz), conventional and trunked two-way radio (VHF, UHF, 700 and 800 MHz), and aircraft position broadcasts (ADS-B at 1090 MHz). None of those can reach a phone, whatever app it runs. On a Raspberry Pi, with free decoders, the dongle turns those into named hits and, for unencrypted digital voice, audio. What Scanner does with it.
An RTL-SDR does not reach 2.4 GHz, so it does not replace the phone or the ESP32 for Bluetooth and Wi-Fi. The two halves complement each other.
At a glance
| What you want to notice | Phone alone | + ESP32 | + RTL-SDR |
|---|---|---|---|
| Bluetooth item trackers | Yes | Further | — |
| Drones with Remote ID | Yes (long-range mode depends on phone) | Further | — |
| Body cams, dash cams, plate-reader hotspots | Yes, between scans | Sooner, on fixed channels | — |
| Tyre sensors, key fobs, 433 MHz sensors | No | No | Yes |
| Two-way radio, trunked P25 and DMR | No | No | Yes (encrypted calls stay encrypted) |
| Aircraft (ADS-B) | No | No | Yes |
| Spectrum view below 1.7 GHz | No | No | Yes |
| Cellular GPS trackers, GPS loggers | Not identifiable | Not identifiable | Not identifiable |
What none of them do
Everything here is receive-only. Nothing transmits to, connects to, or jams anything. Nothing decrypts encrypted radio. Nothing detects radar or speed-enforcement equipment. And a device that is switched off, or simply not broadcasting, is invisible to all three. Measured results and known weaknesses has the numbers we have so far.
How to choose
Start with the phone. If you mostly drive and want alerts a little earlier, add an ESP32. If you want the sub-GHz world (sensors, radio, aircraft), that is what an SDR is for. Every one of them can be built from the guides on this blog, or bought set up and tested in the shop.
Order it today, drive with it this week
Every unit is flashed, set up for the area you give at checkout and tested before it ships. Free shipping in the US, $25 flat everywhere else, updates free for life. The Spotter ships cased; Full Spectrum is the whole car in one box.
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Open firmware and bridge on GitHub · receive only · every command on this blog is copied from a Pi we run