Google Home users started receiving alerts when their fire alarms went off or their plates smashed in their homes. Google acknowledged that it accidentally rolled out a feature causing the smart devices to record sounds without the voice prompt. Reports of the privacy faux pas began after one Reddit user reported that Google sent him a phone notification saying that the smoke detector in his home had been triggered. Google for its part said that the alerts are part of a subscription service called Nest Aware, first launched in May. The service allows users to pay for the devices to detect any critical sound in their home and send them an alert on their phones.
Source: https://threatpost.com/google-fixes-mysterious-audio-recording-blip-in-smart-speakers/158219/