Desert Star Systems makes a locator/pinger model for diving. They have two models: the
Sport & Scout
From their website: DiveTracker Sport and Scout are simple, yet very effective, underwater homing systems. Designed originally for sport divers, these devices have found a variety of applications in underwater commercial and military ventures, law enforcement and science. Typical tasks include marking of underwater objects, safeguarding and recovery of underwater instrumentation and vehicles, general diver navigation and emergency pingers for divers.
The chief attractions of these devices are ease of use, low cost and operational reliability due to their simplicity. Both systems consist of two components, a transmitter (pinger) and a receiver. Using the indicators on the receiver, a diver can easily return to any location or object marked with a transmitter. To aid in the return to a boat, the transmitter may be lowered from the boat or attached to the anchor line. To serve as a distress beacon, the transmitter can be carried by a diver, to be activated when an emergency occurs. A diver can carry transmitters, then use them to mark underwater object or locations for a later return. Any number of receivers can be used with one transmitter, allowing a group of divers to use the system.
You can buy direct from them or
Leisure Pro carries the Scout. Due to low visibility in my local lakes I'm buying one of these to aid with navigation.