WARNING: THIS CIRCUIT IS CONNECTED DIRECTLY TO THE MAINS SUPPLY AND CAN BE DANGEROUS. EXTREME CARE SHOULD BE TAKEN AT ALL TIMES WHEN WORKING AROUND LIVE MAINS VOLTAGES TO PREVENT ACCIDENTAL ELECTRIC SHOCK. THIS PROJECT IS NOT FOR BEGINNERS. IF YOU ARE NOT CONFIDENT WORKING WITH AC MAINS VOLTAGES, THEN THIS PROJECT IS NOT FOR YOU.

There are more stylish looking momentary switches that look good on a front panel as a power switch than there are latching ones; some with LED rings, others with the "on/off" symbol that light up. There's just one problem. They're momentary. This circuit allows the use of a momentary switch as a power switch to turn on or off a main power transformer in a product/unit.

Based on a bi-stable 555 timer flip-flop, pressing a button will turn on the relay allowing the main transformer to be energized. Conversely, hitting the same button again will turn it off. Pressing and holding the button in will only make it change state once, ie: it won't oscillate on and off.

A more in-depth explanation of the circuit operation is described in the linked video below: