Hello @LarsBram, welcome to Sonos Community!
Here is a very helpful Support Article: Pair Sonos Era 100 with Bluetooth. In there you will find the below information.
Era 100 has an Idle Auto-Disconnect setting which will disconnect your Era 100 from a Bluetooth device after 30 minutes of sitting idle. This setting is off by default, but can be turned on in the
Settings tab under System → Era 100 → Bluetooth → Idle Auto-Disconnect.
Make sure the Idle Auto-Disconnect is disabled. Something else worth mentioning is that the volume of the beep on Bluetooth connection/disconnection depends on the volume of the speaker itself during that process.
It would be nice to be able to disable this acknowledge sound and just rely on the blue/white light.
I’ve marked your thread as a feature request and forwarded it to the appropriate teams for consideration.
Thank you for the feedback and I hope the above helps.
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