Siren Marine Canvas Snap Cover Sensor Wired. When the normally closed alarm circuit is opened it triggers an entry alert to the boat owner and can also be rigged to sound an audible alarm. A snap cover sensor is a perfect solution for stopping unwanted access to the boat and expensive parts. Specifications for Siren Marine Wired Canvas Snap Cover Sensor: Manufacturer: Siren Marine Color: Black Package Contents: Siren Marine Wired Canvas Snap Cover Sensor Siren Marine SM-ACC-SNAP: Canvas Snap Cover Sensor Wired