Abstract: An event detection and localization system is provided that employs a plurality of smartphones. The detected events may comprise a gunshot, a biological threat, a chemical threat and/or a radiological threat. Each smartphone comprises a memory for storing an event detection process; and at least one hardware device to implement the event detection process. The hardware device is operative to detect an event based on a signal obtained using a sensor in the vicinity of the smartphone; obtain a time of arrival of the signal; obtain a location of the smartphone at the time of arrival; send a notification of the arrival time and arrival location to one or more of another smartphone and a server; and receive an indication of an origination of the event.