Your Alert should be "Device Monitor - Device Monitor System Connectivity" if you have your "Configure Device Monitoring" setup, if I am not mistaken.
If you just need a report sent out daily of devices that rebooted then you can find that in the Inventory - OS - NT Info - Last Boot Up Time and you can create a LD Query based on date (<=GetDate() -1 which means yesterdays date) and then right-click and create a Report and Schedule it to email daily.