US Patent 10595400 Tamper detection system

A payment reader includes a tamper detection system having a first sensor element disposed on a circuit board of the tamper detection circuit; a second sensor element disposed within an interior surface of a housing of the tamper detection circuit; and a guard ring disposed on the circuit board of the tamper detection circuit configured to form an electrical connection with the first sensor element in response to injection of conductive fluid thereby indicating tampering with the tamper detection circuit, wherein the guard ring is configured to be on a plane different from the first sensor element to prevent unintentional activation of the tamper detection circuit.