The Beoplay A1 will automatically switch off after 15 minutes to preserve battery life if it does not detect an audio signal.
However, installing the latest software update will allow you to keep your Beoplay A1 switched on while having a source connected through the Line-In connection provided the Beoplay A1 is connected to the charger.
For more details on how to update the software of your Beoplay A1, click here.