The Pebbles do not have a specific 'turn off' button. Instead, they are designed to go into a low-power sleep mode when not in use.

1. Finish Your Session: After completing your breathing exercise, the Pebbles will naturally conclude their active mode.
2. Leave the Pebbles Idle: If you just leave the Pebbles untouched after use, they will automatically go into sleep mode after a period of inactivity. This is a power-saving state where the device uses minimal battery.

Note: If you're planning not to use your Pebbles for an extended period, it's recommended to store them in a cool, dry place and perhaps give them a charge now and then to keep the battery in good condition.