One or more sensors gather data, one or more processors analyze the data, and one or more indicators notify a user if the data represent an event that requires a response. One or more of the sensors and/or the indicators is a wearable device for wireless communication. Optionally, other components may be vehicle-mounted or deployed on-site. The components form an ad-hoc network enabling users to keep track of each other in challenging environments where traditional communication may be impossible, unreliable, or inadvisable. The sensors, processors, and indicators may be linked and activated manually or they may be linked and activated automatically when they come within a threshold proximity or when a user does a triggering action, such as exiting a vehicle. The processors distinguish extremely urgent events requiring an immediate response from less-urgent events that can wait longer for response, routing and timing the responses accordingly.