Ford Key Fob - low battery

[Barry Floyd]

My wife's Nissan Pathfinder has a thing built in where if the battery on the key fob is completely dead, you can take the fob and just hold it up against the start button and it will magically read the fob to start the car. No clue how that works, it just does.

[Frank Cox]

There's actually a notch on the right side of the steering column in my Escape where you put the key to start it if the key battery is dead.

I looked that up in the manual when all of this was going on, just in case.

Ultimately I didn't actually need to know that, though.

[Lyle Romer]

My wife's Nissan Pathfinder has a thing built in where if the battery on the key fob is completely dead, you can take the fob and just hold it up against the start button and it will magically read the fob to start the car. No clue how that works, it just does.

The FOBs communicate with some type of near field communications protocol similar to RFID. The battery allows the FOB to transmit at high enough power for the vehicle to receive the data far from the antenna. If you hold the FOB up to the antenna (which in the case of the Pathfinder must be behind the start button) it transmits (well, reflects) passively like an RFID card or tag.