This guide closes the gap that lets thieves relay your car key's signal from inside your home to your car. You will block the signal from every key you own, test that it works, use your key's sleep mode or turn off keyless entry where your car allows it, and lock down phone-as-key apps. Plan on 30 to 45 minutes, plus a few minutes of reading in your owner's manual.
Why bother
Keyless entry unlocks your car when it senses your key about a metre from the door. A relay attack fools that check. One thief stands near your house with a device that picks up your key's signal, even through a wall or front door, and passes it to a second device held next to your car. The car thinks the key is right there, so it unlocks and starts. Nothing is broken and often there is no alarm. Police say thieves only need to get within a few metres of your key. The fix is to make sure there is no key signal for them to pick up, or to stop the car accepting one without a button press.
Before you start
- Time: 30 to 45 minutes.
- You need: every key for the car, including spares. If you use your phone as a key, you need the phone too. You also need your owner's manual (printed, in the car's touchscreen, or on the maker's website), and one signal-blocking pouch or box per key. Buy pouches made for car keys and test them (Step 2). Tests by a tracking company found cheap ones often fail.
- Know your fallback: find the mechanical key blade hidden inside your fob and learn how to use it on the driver's door. You may need it if you turn off keyless entry and then the fob or car battery goes flat.
- Checked on (2026-10-15): Google Wallet car key help (Android 12 or later), Apple Wallet car key help (current iOS), Samsung Wallet Digital Key help and Ford's online owner's manual. Ford, Toyota, Mercedes-Benz and Tesla steps come from the makers' published support text; confirm them in your own manual, because sequences differ by model, year and market.
Steps
1 Gather every key and put each one in a signal-blocking pouch
- Find every key: the one you use, the spare in the drawer, and any key a partner or family member keeps.
- Put each key fully inside its own pouch or a lined box, and close the seal or flap all the way. A fold-over pouch only works when it is folded over.
- Choose one place to keep keys at home. It should be away from the front door, windows and the wall nearest the car. Distance does not replace the pouch, but it helps.
You should see every key you own accounted for, each in a closed pouch. A single spare left on a hall table defeats the rest.
2 Test each pouch at the car
- Make sure the car is locked.
- Put a key in its pouch and seal it.
- Hold the pouch and stand right next to the driver's door. Pull or touch the door handle the way you normally would to unlock.
- Try the boot or tailgate handle as well.
- Repeat for every key and pouch.
You should see the car stay locked and show no reaction. If it unlocks, that pouch does not block the signal. Replace it and test again. Retest every few months, because linings tear and seals wear out.