Amazon adds further capabilities to Echo devices with the introduction of 3 APIs-- Doorbell Event Source, Motion Sensor and Alexa.RTCSession Controller, allowing developers to connect the devices to security cameras and doorbells.
Initially available in the US as part of the Amazon Smart Home Skill API, such features allow 3rd party smart home apps to trigger Alexa actions through doorbell presses and motion alarms, among others. The Doorbell Event Source API plays announcement across all Echo devices, while Motion Sensor reports the state of an endpoint whenever motion is noticed within an area.