Systems (100) and methods (1400) for verifying a detachment of a security tag (108) from an article. The methods comprise: producing by a detaching unit (106) a first signal at a first frequency and a second signal at a second frequency when the security tag is in proximity thereto; generating, by a non-linear electrical circuit (504) of the security tag, a third signal from the first and second signals applied thereto; ceasing generation of the third signal by the non-linear electrical circuit when at least a first portion (306) of the security tag is moved a certain distance from the detaching unit; and determining by the detaching unit that the first portion of the security tag has been decoupled from a second portion (318) of the security tag when the third signal is no longer being generated by the non-linear electrical circuit.