so i’m at cvs and im walking to the bathroom and see this on the floor right before i walk in. (Pic 1)

And i pick it up cause i thought, what a cute lil tank circuit. Wonder what it’s doing here? well after i bought my stuff and went to leave the store, the alarm goes off. and im like ‘so thats what it is.’

it got me curious at what kind of circuit and sensor set up these cvs alarms got that a simple tank like this (presumably precisely tuned) would trigger the alarm?

obviously, the door alarms have a device and circuit inside that producing an alternating magnetic field. when someone walks through the gates with stolen property from the store containing when these little tanks circuits set off the alarm. Seems safe to assume that the resonant frequency of this LC circuit is probably tuned to the frequency of the alternating magnetic field coming from the antitheft alarms in the doorway of the store.

So anybody have a suggestion what is simple circuit that’s based off of the principal that these works off of would look like? sorry I’m using voice to text. I guess what I’m saying is come up with the circuit that would set up an alarm if this were to pass through it th Sorry I’m using voice to text. I guess what I’m saying is come up with the circuit that would set up an alarm if this were to pass through it. that’s my challenge to you.