Smart keys are brilliant when they work — and infuriating when they don't. 'Key not detected' is one of our most common keyless-car callouts across West London.
Cause 1 — flat fob battery
Even a half-dead CR2032 will trip 'key not detected' randomly. Always the first thing to try — under £3 and a 30-second job.
Cause 2 — failed keyless antenna
Modern cars have 4–6 LF antennas around the car. One failure causes intermittent 'no key' depending on where the fob is in the cabin. Diagnosed with live LF signal data.
Cause 3 — water-damaged fob
Pockets sweat, laundry happens. Even minor corrosion on the keyless transponder PCB causes intermittent detection. Sometimes repairable, often a new fob.
Cause 4 — comfort access module fault
On VAG, BMW and Mercedes the keyless module itself fails. Coded module replacement is usually mobile, not a dealer-only job.
How we diagnose mobile
Live LF antenna scan + fob radio test in 20 minutes at your driveway. No guesswork, no parts cannon.
Related services on StageMyCar: keyless car specialist in Slough and replacement smart key service.