To prevent unnecessary actuation of a power circuit of a key entry system, which is in a non-operating state.

A key entry and security system having a passive signal discriminator for decreasing erroneous starting of a power consuming circuit, is comprised of an interrogator, a receiver, a starting logic, and an asymmetric time constant low-pass filter interposed between an output from the receiver and an input from the starting logic. If a first signal is present in the asymmetric time constant low-pass filter over a desired period of time, a second signal is generated from the asymmetric time constant lowpass filter. On the other hand, if the first signal is not present over the predetermined period of time, the second signal is not generated.