Low Power Time-base

The oscillator from a kitchen-type clock can be used to generate a 0.5Hz negative-
going pulse, for example as an interrupt to wake the PIC from SLEEP or to drive
CMOS dividers. Disconnect the clock's coil and ground either of the chip's two outputs.

In normal use, the two outputs cause a reciprocating or alternating-polarity magnetic
pulse in the coil to rotate a small magnet on the seconds-hand gearing and advance it

See also How To in more detail