Self-detaching anti-theft device with energy limit

A method for operating a security tag, comprising:

• inducing a voltage in a receive circuit of a security tag via a first wireless signal;
• closing, by a controller of the tag, a switch thereby allowing energy to flow from the receive circuit to a mechanical component of the tag;
• determining, by the controller, when an accumulated amount of energy dissipation by the mechanical component from the flowing energy exceeds a threshold value;
• and
• opening, by the controller, the switch upon determining that the accumulated amount of energy dissipation by the mechanical component exceeds the threshold value.

A security tag, comprising:

• a receive circuit, operative to receive a first wireless signal and in response develop a voltage across the receive circuit;
• a switch connected in electrical series with a side of the receive circuit;
• an electro-mechanical lock electrically connected across the switch and the receive circuit;
• a controller operative to:
• selectively open and close the switch, thereby controlling energy flow from the receive circuit to the electro-mechanical lock;
• upon closing the switch determine when an accumulated amount of energy dissipation by the electromechanical lock from the flowing energy exceeds a threshold value;
• and
• upon determining that the accumulated amount of energy dissipation by the mechanical component exceeds the threshold value, open the switch.