The new ACR Satellite2 406 MHz EPIRBs are far more reliable locating devices than the older Class A and B devices. The signal from a 406 is stored by a COMSAT satellite until the signal is received by at least two other satellites, at which time your position can be triangulated. In effect, the 406 signals your position as well as your vessel's registered name, type, size, and who authorities should contact.
The accuracy of a 406 EPIRBs is greater, and its dependability is superb. The older Class A and B (243 MHz) EPIRBs are unlikely to provide a satellite fix; they are largely dependent on shore stations to receive their 121.5 MHz signal. Consequently, their capabilities for offshore use are limited. And, while there are plenty of stations in North America, there are few elsewhere in the world.
We recommend Class A and B EPIRBS for near-shore use only. All vessels going offshore should use a 406 MHz Category I (float-free deployment) or Category II (manual deployment) EPIRB. The 406 broadcasts simultaneously on 406 MHz, 243 MHz, and 121.5 MHz, making your position known on both civilian and military homing frequencies.
It has a full self-test mode and battery indicator. Its lithium battery has a 10-year shelf life. The ACR 406 is rugged and dependable, and we recommend it for everyone who ventures offshore. Replacement EPIRB Antennas available.
Category I Automatically Deployable 2774NH (2774) Cat.1 (RLB-32 CAT I) Automatically Activated: Unit with Hydrostatic release mechanism. Stationed outside the pilot house, this unit will deploy and activate automatically if the vessel sinks. Required on all commercial fishing vessels. (look here for the replacement hydro)