The Pebbles are designed to automatically switch to an energy-efficient sleep mode after a period of inactivity. When you're done using them, just put them aside for a while and they should go into sleep mode on their own.
If your Pebbles doesn't shut down or goes into sleep mode as expected, here are some steps to fix the problem:
If the problem persists, please contact Glimp Customer Service for further assistance. We can provide more in-depth troubleshooting or advice on the next steps, possibly including a warranty claim if necessary.