Suunto D5 has water contact functionality that recognizes when the device is in contact with water. When submerged, the water contact poles are connected by the conductivity of the water.
Suunto D5 switches to dive state when water is detected. Dive starts
A wave icon appears on the left, above the ascend indicator when the device is under water. See Display - modes, views, and states for an overview of dive screen icons.
Water contact icon:
Water contact icon in Free mode Depth view:
If you see a question mark in a yellow square appear, that means the device is functioning abnormally. E.g. it can signal that the water contact is not working as expected. Start using your backup instrument, abort the dive immediately and safely ascend to the surface. Call Suunto Customer Support and return your computer to an authorized Suunto Service Center for inspection.