alarm with resistor

[andrew2022]

is it possible 2 have an alarm, were the alarm is switched on/off wen a certian value resistor is inserted (e.g, the resistor is in a key, so wen the key is inserted the 2 contacts make contact with the alarm, the alarm measures the resistance nd if itz within a certian resistance, the alarm is switched on/off)

 

[Russlk]

Easy to do. Do you have another question?

 

[andrew2022]

Easy to do. Do you have another question?

yes. how?

 

[magickaldan]

Thats basically what my car has. I don't know how it works but the key has a tiny resistor on it, and when the resistor is inserted it allows the car to start but if the resistor is not there it would not allow the car to pump gas.
So if someone tried to steal the car and pick the lock or break the lock the car wouldn't start without that specific resistor. My guess is they use somekind of PIC.

 

[Sebi]

Just use a window-comparator and delay (to prevent with potmeter opening)