Determining if a hermetically sealed MEMs device loses hermeticity during operation. In one embodiment, the MEMs device is an accelerometer. A test signal having an associated frequency above an operational frequency range for the accelerometer is provided to the accelerometer at an input during operation of the accelerometer for sensing an acceleration. The output signal of the accelerometer is filtered at least above the operational frequency range of the accelerometer producing a test output signal. The test output signal is then compared to a predetermined threshold to determine if the amplitude of the test output signal differs from the threshold. If the amplitude of the test output signal differs from the predetermined threshold, an error signal is produced indicating that hermeticity of the accelerometer has been lost.