One of the best ways to protect against electrical shock in your home is to install ground fault circuit interrupters, commonly called GFCI's for short. These devices monitor how much current flows to an appliance on the hot wire and how much comes back on the neutral wire. If the difference is greater than 0.005 amps, a fault is detected, and the GFCI will interrupt the power in a fraction of a second. This level of current has been selected because it is above the human level of perception of electricity but well below the "let-go" level, where loss of muscle control occurs.
A GFCI outlet has two buttons on the front: a reset button and a test button. When the test button is pushed, an internal short is placed across the GFCI outlet and should cause the GFCI to trip and shut the power off. The reset button should pop out when this happens, which helps alert someone that the GFCI has operated.
The GFCI is re-energized or "re-set" by pressing in the "reset" button. If the reset button will not hold and the GFCI continues to shut the power off every time the reset button is pushed, this indicates there may be a serious electrical problem that needs attention.