The Signal Sidearm is a sensor designed to be fitted to a police pistol holster: when triggered, it wirelessly signals all nearby police bodycams to go into record-and-archive mode. It's made by Axon, the bodycam division of Taser International.
Signal Sidearm joins two other "Signal" products. Signal Vehicle can be configured to broadcast a wireless "start recording!" message when the car door opens, or when the police lights or siren are activated. And the Signal Performance Power Magazine is a replacement battery pack for the Taser X2 and X26P that tells nearby cameras to start recording when the weapon is armed, and also logs the exact moment the trigger is pulled.
The whole point of the Axon Signal tech is to hopefully increase the reliability of police body-worn camera footage. If the cameras start recording at pre-defined triggers, require little manual intervention, and there is redundancy built into the system via multiple sensors—siren, car door, holster, magazine—then there's a lower chance of an incident not being recorded.
New holster forces all nearby body cams to start recording when gun is pulled
[Sebastian Anthony/Ars Technica]