Lets you check the housing's water-tight integrity before diving. Althoug small size, the Sentinel V5 is equiped with a pressure sensor built-in LED along with an external vacuum pump. The pump creates a vacuum inside the housing, the sensor detects any leaks and the lights let you know if it is safe to dive or not. LED flashes red and green when the housing leaks air. LED flashes green when the housing does not leak. Compatible SEA&SEA Housing - Canon: - (SS-06181) MDX-5DMK IV - (SS-06180) MDX-80D - (SS-06175) MDX-7DMK II - (SS-06174) MDX-5DMK III v.2 - (SS-06169) MDX-70D - (SS-06166) MDX-6D - (SS-06163) MDX-5DMK III - Nikon: - (SS-06179) MDX-D500 - (SS-06173) MDX-D810 - (SS-06167) MDX-D7100 - (SS-06165) MDX-D600 - Sony: - (SS-06182) MDX-a6300 - (SS-06176) MDX-a7 II Inlcudes manual pump and bettery.