Please provide more details. Are they playing music by themselves? From what source?

1. you’ve set an alarm;
2. someone else is logged into your system;
3. a Spotify link has not been broken and someone doesn’t realise they’re still linked to your speakers;
4. a different reason.

Technically, I think 1. needs to include alarms set on the Sonos device by external apps, too. 

I will check this out thnks 

Are you using Sonos Voice Control (SVC) or Alexa? If so, one or both may be the issue as they can both be activated simultaneously on the Era series. Sometimes a voice assistant will pick up a conversation sound and think it’s a command to play. My Era 300’s with SVC are sometimes prone to start playing without a direct command. The oddity may just be inherent to voice assistants in general; but can be annoying.

Thanks for the response, I believe it is alexa or sonos voice