An optical module includes an enclosure and an optical output assembly mounted on the enclosure. An emitter mounted in the enclosure is configured to emit a beam of light toward the optical output assembly. A connector, which includes two conductive layers separated by a dielectric layer, has a first side connected to the enclosure and a second side connected to the optical output assembly. An electrical trace disposed on the enclosure is connected to the first side of the connector so as to define a test circuit having a capacitance. Control circuitry is coupled to sense the capacitance of the test circuit, and configured to inhibit operation of the emitter upon sensing a change in the capacitance that exceeds a predetermined threshold.