A Fluke clamp meter.

Is it advisable that low voltage security installers carry a Hall Effect meter at all times?

Yes, you could make a strong case in favour of this. Clamp-on (Hall Effect) meters measure currents up to 1000 amps (a standard DMM only goes up to 10 amps). While they are not as flexible as a DMM, clamp-on units will also measure voltage and while they’ll do it with a little less accuracy than a direct circuit connection, they’re a lot safer to use.

These devices are ideal if you’re testing a conductor with current flowing in one direction – you can place the tester perpendicular to a magnetic field and a voltage can be measured at right angles to the current path. The beauty of a clamp-on meter is that it allows you to establish AC power delivery in nearby AC cables so you can be alert to EMI radiation.

A Hall Effect meter also allows you to check for live wires in your work space and make informed decisions about possible faults on system-connected AC circuits without needing an electrician to open an AC cable jacket or break AC connections. A clamp meter can also tell you if an AC power outlet is live.