Multicomp panel mount alert emits a pulsating electronic 80dB sound when 3VDC up to 12VDC is applied. Totally self contained. Mounts in a 1.1" diameter hole with included ring nut. Has three screw terminals on back to connect power (Pulsating -Continuous -, & +. Overall size is 1.67" diameter x 1.31" deep (excluding terminals)