Cateye Strada Smart CC-RD500B Online Manual page 121

When the smartphone moves away from the bicycle even for a
short time, Strada Smart may automatically enter sleep mode.
Clicking Strada Smart will make it enter smartphone search
mode, allowing you to reconnect to your smartphone.
Sleep
Strada Smart operation is abnormal. What should I do?
Restart your smartphone.
If this does not resolve the issue, press the AC button
on the back of Strada Smart. (Restart operation)