A method of leak detection of hermetically sealed cavities semiconductor devices is provided. Scribe streets are formed with access from each packaged device on a first substrate to the edge of the first substrate. The first substrate is attached to a second substrate, forming gaps between the two substrates. A cavity is formed around a packaged device on the first substrate by attaching a bond ring to the first substrate and an optically transparent window above the bonding ring. The cavity is evacuated. A high powered laser beam strikes the top surface of the device on the first substrate within the cavity and creates a vertical surface displacement of the first substrate. The vertical surface displacement is monitored using a separate interrogation laser beam. Leakage of the cavity can be measured by characterizing the resonance decay rate, Q.