Finding lost key fob

Does anyone know if there is a type of sensor that I could use to detect the exact location of a key fob that is lost within my vehicle? Seriously. The Intelligent Key for my Murano fell out of my pocket and slid under the driver’s seat while I was driving. While looking for it later, I think I pushed it under the carpet, through the opening for the ventilation tube. It is definitely in the vehicle, as the doors won’t lock and the ignition will start. I cannot find it after a lot of searching. I asked the dealer if they had a sensor to find it, and they said good idea but such device does not exist. They could not find the key fob, either, even after removing the driver’s seat. Before I have them deactivate it, I want to see if anyone knows whether it emits a radio signal that could somehow be detected?

I have no knowledge of such things, but I can suggest a low tech solution. Stop by an auto parts store and find a magnetic pickup - basically a magnet on the end of a stick - probe around all of the areas that it may have gone and you just may come up with it. These magnets are usually pretty strong and you wouldn’t necessarily need to make actual contact with the key.

Of course, you might first want to find out if the contact with a magnet would mess with whatever microprocessing stuff is in there.

Why, yes, it does emit a radio frequency in response to the polling of the car’s immobilizer system. You ask the car to start by pressing a button the immobilizer system wants to see some credentials and sends out a summons to the key fob. The key fob responds. There seem to be a range of frequencies used by key fobs, including 315 MHz, 418 MHz, and 433 MHz.

Linx technologies manufactures OEM-compatible aftermarket transmitters and receivers. You might consider contacting them or someone like them for advice.

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Thanks to both of you. I will look into your suggestions.

It only transmits when you hit its buttons.

Sorry, but other than possibly snagging it with a magnetic “pickup tool”, available at any parts or hardware store, pulling the seat is the only way to get there from here.

I am having difficulty envisioning the scene where the key got pushed into a pocket. If practical, try to get it out with a shop vac. If the nozzle itself does not work, use some thinner vinyl tubing attached to the nozzle with duct tape. How thin? I don’t know. Pick up some short lengths of different diameters and try them out.

Is it the fob with the battery that is signaling the car or the key (no battery) itself. If the latter it must gets its power by induction by an outside field and transmit with that power. Theoretically, there is a way to find it with an inducer and a receiver of the correct frequencies. It would take some serious thought, knowledge and equipment to find it in the manner that you suggest. A smart ham radio operator that is versed in antenna design might be a good source of help.

I’m sorry but I think you have to look a little harder. Pull the seat out again or both if it is a bucket, and have a look with a bright light. You may need to slit the carpet a little to get at it, but just do it the easy way and look hard for it.

This is a long shot, but it may work. Get a piece of sheet metal, maybe 6 by 6 inches, and place it over various spots in the floor to block the signal from the key fob. If the doors lock, the metal is over the fob.

No need to cut the carpet, just remove the trim panel at the carpet edge and lift up. The kick panel may have to be removed to get at the front screw/fastener but those are usually easy to remove as well. Then you can look between the carpet and backing or backing and floor for the lost FOB.