SPOT is a satellite messenger that uses private industry communications satellites and a private industry emergency communications center. A PLB is a device that signals government-owned and operated satellites that are part of the COSPAS-SARSAT system. Signals are then sent to rescue coordination centers, which in the USA are operated by the USAF and USCG.

A PLB will work if it's registered, and there are no subscription fees. SPOT requires a subscription to operate.