The external shutter is designed to control the camera shutter underwater to take  pictures, video and even access third party photography apps by Bluetooth underwater.
 
Can be used both on Land and Underwater
Multiple Installation options; can be installed direct to SeaTouch 4 housing or to a camera tray (fits the Dive Lantern CT25 and CT35 camera trays)
Ultra-low Power Consumption Operation
Low-frequency operation sleep mode for power saving, automatically powers off after 10 minutes of inactivity
Rigorously tested for longevity
Over 100,000 Keypress Tests
Withstands 60m Water Pressure
Waterproof down to 200 FEET (60M).
Compatible with Android and iPhone smartphones