Is it possible to have a circuit that does something (fires a pulse, turns on a voltage, whatever) when it detects a radio signal at a specific frequency? One crucial point is that it should do this without recourse to any sort of clock within the circuit (which rules out logic gates, standard digital ICs, etc., I believe). I would need the frequency it detects to be within unrestricted frequencies (i.e. no government restricted ranges).
I'm not too fussy about the frequency detection being super accurate, as long as it detects within a relatively small frequency band - with extra points for being able to change that frequency, though that last is not essential. I'm also not too fussy about any specifics of that radio signal (I'm fine with it being a pulse, an oscillating volume, a consistent signal, or whatever), though a reasonable degree of sensitivity to a low power signal would definitely be useful.
I'm also not too fussy about power usage, though low power usage would definitely be useful.
I mainly need to know if that is possible, though of course anything you can tell me about what that would look like would be much appreciated.