Most tests using a multimeter involve low voltage and resistance, both of which can’t hurt you much. But sometimes you may need to test high voltages, such as the input to an AC-operated power supply. In a case such as this, careless use of the multimeter can cause serious bodily harm. Even when you’re not actively testing a high voltage circuit, dangerous current may be exposed if you work on certain electronics equipment, such as a radio, hi-fi, or VCR.
If you ever need to work with an electronics project that uses house current (117 volts in the US; 220 volts in many other countries) and you touch a live AC wire, you can seriously hurt or even kill yourself. Always exercise caution when handling electronic equipment and electric wires. Be especially careful to keep your fingers away from the metal tips of the meter test leads. The test leads are the wire probes that you use to connect the multimeter to your circuit. If you handle the probes carelessly during testing you may get a serious shock.
Never blindly poke around the inside of a circuit with the leads of a multimeter in an attempt to get a reading. Apply the test leads only to those portions of the circuit that you are familiar with. One safe method for using a meter is to attach a clip on the black (negative or common) lead and connect that lead to the chassis or circuit ground. Use one hand to apply the red (positive) lead to the various test points and stick the other hand safely in your pocket. With one hand out of commission, you’re less likely to receive a nasty shock, even if you aren’t watching what you’re doing.