The ACR HemiLight 3 — a compact survivor locator light that switches itself on when it hits water.

Automatic activation is the whole design. Someone going into the water unexpectedly, at night, is not in a position to find and operate a switch — and that is precisely when being visible decides the outcome.

Mounts to a lifejacket or PFD and then is ignored until the day it matters. Long battery shelf life, nothing to maintain.

Required or recommended on lifejackets in many boating contexts, and worth having on any PFD used after dark.

If there is a boat, a raft or a paddleboard in the plan, this belongs on the vest.