- Can I trust it to tell me a circuit is dead?
Use it the way an electrician would: test a source you know is live, then test your circuit, then test the known-live source again. That last step is what proves the tester was working the whole time. Be straight with yourself about the limits — any non-contact tester can read low through shielded cable, metal conduit or a deeply buried run, so it is reliable for telling you something is live, and it is not a replacement for isolating the circuit at the consumer unit and locking it off.
- What is the difference between the two modes?
Non-contact senses the field around a conductor without touching it and covers 30 to 1000 V — that is the mode for a first check on a socket, a fitting or a cable. Contact mode puts the tip on the conductor and reads 11 to 450 V, which covers lower-voltage work like automotive and appliance circuits. Both are for 50–60 Hz AC.