How do you "ping" a modern car keyfob?

This has no malicious intent. But in my household, keys sometimes disappear, in one case not to be found again until six months later.

Now the new car (a Honda) can tell whether a keyfob is nearby. This means the keyfob is either constantly transmitting a low power "I'm here" signal, or it is constantly listening at low power for an interrogation signal.

This means it should be possible to "sniff" for the keys' presence. Only presence! Not whatever rolling unlock code would allow the car to be used. But this means one could have some help locating them in the house by just repeatedly transmitting the interrogation signal and listening for a reply.

Is there any knowledge out there to do this? With an RTL-SDR or a Flipper Zero or whatever? That is not tied up in criminal car thieving contexts?