The Apple Watch has a number of sensors that can monitor the wearer's environment. A patent application by Apple describes using the information from the sensors to determine when an emergency exists so help can be summoned.
See related: "Siri, I've fallen and I can't get up!"
According to the patent application, events include health issues such as heart attacks, accidents with injury, and even muggings. These can be detected through a combination of sensors, e.g. sudden stops in the accelerometer combined with a lack of heartbeats.
The system is a two-step process. First is the detection of an emergency event, followed by a tiered notification system designed to prevent false alarms. This system could notify designated family members first, followed by a 911 notification to emergency personnel.
A wearable with various sensors is the perfect platform for such a system as they are always with the affected party. In the case of the Apple Watch, the integration with the iPhone makes it a full communication device for summoning help.
This is a good use case scenario for the Apple Watch that can provide benefit to owners when they need it most. Should this come to fruition it could even be an option for those seeking peace of mind for elderly family members. "Help I've fallen and I can't get up" could automatically summon help, even if the affected party can't do so.