The clock itself is an off-the-shelf timepiece purchased from Target for the princely sum of $5. However, it’s been deviously modified with an RP2040 microcontroller hidden away inside.

This allows the microcontroller and RTC module to run from the clock movement’s 1.5 V AA battery. [Josh] estimates a current draw of about 6 μA per day, which works out to about 50 years from a ...