How to tell if an AirTag is tracking you, and how to find it

Most people never have a problem with trackers. But if you keep getting "unknown accessory" alerts, or you simply want to check your car and bags, it helps to understand what these devices actually transmit and how to find one.

01Warning signs that a tracker is following you

• Your phone shows an alert such as "AirTag Found Moving With You" on iPhone or "Unknown tracker traveling with you" on Android.
• You hear a short chirp from your bag, coat or car and cannot find where it comes from.
• Someone seems to know where you have been, in a way that does not match what you have shared.
• A small round object or a slim card appears in a place you did not put it: bag lining, jacket pocket, under a car seat, inside a bumper or wheel arch.

02What your phone already does for you

Apple and Google agreed on a joint specification called Detecting Unwanted Location Trackers (DULT). Both iOS and Android listen in the background for trackers that are separated from their owner and moving with you over time.

Phone alerts are deliberately conservative. They wait until a tracker has been near you across several locations, to avoid false alarms from your friends' keys. That delay is the gap a manual scan fills.

03How Find My trackers broadcast

An AirTag has no GPS and no mobile connection. It sends short Bluetooth Low Energy advertisements. Nearby Apple devices hear them, encrypt the location of the phone that heard them, and upload it. Only the owner can decrypt that location.

For detection, the useful detail is the format of those advertisements:

• The manufacturer data starts with Apple's company identifier, 0x004C.
• The next byte is the message type. 0x12 is the "offline finding" message, which a tracker sends when it is away from its owner.
• The Bluetooth address rotates periodically, so you cannot simply note an address and look it up later.

So a device sending 0x004C + 0x12 that stays near you while you move between places deserves a closer look. Third-party Find My accessories and DULT trackers use the service UUID 0xFD44, which you can watch for as well.

04Scan for trackers with an ESP32

Any ESP32 with Bluetooth can act as a dedicated tracker scanner. It never sleeps, it does not care which phone you own, and it shows raw signal strength. This sketch prints every separated Find My device it hears, with its RSSI in dBm.

#include <BLEDevice.h>
#include <BLEScan.h>
#include <BLEAdvertisedDevice.h>

class FindMyFilter : public BLEAdvertisedDeviceCallbacks {
  void onResult(BLEAdvertisedDevice d) override {
    if (!d.haveManufacturerData()) return;
    String m = d.getManufacturerData();
    if (m.length() < 3) return;
    uint16_t company = (uint8_t)m[0] | ((uint8_t)m[1] << 8);
    uint8_t  type    = (uint8_t)m[2];
    // 0x004C = Apple, 0x12 = offline finding (separated from owner)
    if (company == 0x004C && type == 0x12) {
      Serial.printf("Find My tracker  %s  %d dBm\n",
                    d.getAddress().toString().c_str(), d.getRSSI());
    }
  }
};

void setup() {
  Serial.begin(115200);
  BLEDevice::init("");
  BLEScan* scan = BLEDevice::getScan();
  scan->setAdvertisedDeviceCallbacks(new FindMyFilter(), true);
  scan->setActiveScan(false);   // passive: listen only
  scan->setInterval(100);
  scan->setWindow(99);
}

void loop() {
  BLEDevice::getScan()->start(5, false);  // 5 s scan
  BLEDevice::getScan()->clearResults();
}

The scan is passive: the ESP32 only listens and never connects to or changes anything. Open the Serial Monitor at 115200 baud, walk around your car or flat, and watch the list.

05Locate it with a hot and cold search

Bluetooth signal strength (RSSI) is a poor ruler at long distances because walls and bodies absorb 2.4 GHz. Up close, though, it rises sharply. That makes a slow hot/cold search very effective.

1. Hold the scanner still for a few seconds at each spot. RSSI jumps around, so look at the average, not one reading.
2. Keep your body out of the line between the scanner and the area you are testing. Your body absorbs a lot of signal.
3. Check common hiding places in a car: under seats, seat pockets, the boot lining, wheel arches and inside the rear bumper.
4. When readings stop rising, search that spot by hand. Trackers are usually coin-sized discs or credit-card thin.

06If you find one

• Read the serial number. Hold an AirTag against the top of an NFC capable phone. A web page opens with its serial number and, in some cases, part of the owner's phone number. Take a screenshot.
• Disable it. Press and twist the back of an AirTag anticlockwise and remove the CR2032 coin cell. It stops reporting location immediately.
• Check again later. Where there was one tracker there may be another.

07FAQ

SGP Lab — written by the team that designs and builds SGP hardware in Europe. We test every example on our own boards before publishing.