A man with one clock knows the time.
A man with two is never sure.
A man with two is never sure.
And a man with a dozen can be driven crazy if each one is off by only a minute or two. So I took my most accurate clock, the GPS Clock and added a radio module that could transmit its time to other clocks throughout the house, wirelessly. Oddly enough, it worked. See video below.
Technical details: GPS clock with UBLOX NEO-6 GPS module, Arduino Nano, nRF24L01+ radio transceiver in the GPS clock, which has both LCD and 7-segment LED displays. Toggle switch sends GPS time to the slave clocks via 2.4 GHz wireless, synchronizing them, with each slave transmitting confirmation back to the GPS Clock. The word 'sync' appears on one and an extra dot on the other, showing successful sync. Also shown: Mini Matrix Clock and Pong Clock. No wires between them, honest.