RescueMe Personal Locator Beacon
The most compact personal locator beacon (PLB). PLBs are the most dependable satellite devices for SOS signalling. They have no subsription costs, but they most be used only when at risk of "loss of limb or life".
Broadcasts SOS to government funded satellite networks (COSPAS-SARSAT), so there's no monthly fee. The PLB weighs 4 oz. (116 g) and it's waterproof (IP-X8).