The safety functions of ground fault circuit interrupters (GFCIs) can fail without notice, so check them monthly. Pick the first or last day of the month so that it is easy to remember.

HOW TO TEST A GFCI OUTLET:

• Find the test and reset buttons.
• Press the TEST button.
• You should hear a snap sound that trips the outlet.

CONFIRM THE POWER IS CUT

• Plug in a lamp or other device.
• The item you plug in should not turn on.

RESET THE OUTLET

• Once you confirm the GFCI is working properly (that the outlet does not work when tested), press the reset button to restore power to the outlet.

RETEST FOR REMAINING SOCKET(S)

You can also buy a GFCI outlet tester that has a display and test button.

GFCI protection can also be installed on circuit breakers to safeguard an entire circuit. They should be tested monthly by pressing the test button on the breaker. If working properly, the interrupter should shut off power to the circuit.

Source: SafeElectricity.org