They need to be engineered to last for a long time between maintenance, be able to withstand the elements (saltwater, sunlight), and it's critical that the unit

They need to be engineered to last for a long time between maintenance, be able to withstand the elements (saltwater, sunlight), and it's critical that the unit functions when you need it. The units are built very tough - mine is waterproof and also floats. The unit has test functions for the GPS and radio, and it has to work for 30+ hours continuously after it's been activated. These things are also regulated by the government and need to meet certain standards.