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The Digital Multimeter

as an Alarm Installation Tool

Digital multimeter by Cen-Tech from Harbor Freight

A  digital multimeter (Also known as a DMM, handheld multimeter, or mini-multimeter) is vital if you do any kind of alarm service or installation. Like its predecessor, the analog multimeter, these meters combine several measuring tools in one.

The typical types of measurements they are capable of making  include:

  • AC Voltage and Current
  • DC Voltage and Current
  • Resistance, measured in Ohms
  • Continuity

While an analog multimeter uses a swinging needle to point to readings on a scale, the digital version shows the measured values with an easy-to-read 7-segment LCD numerical display.

Cen-Tech 7 Function Digital Multimeter with 7-Segment LCD Display Testing a Battery Voltage

Digital Multimeters for Alarm Work

When dealing with home security systems, multimeters are most often used for:

  • Testing backup batteries in alarm panels
  • Checking wireless transmitter batteries
  • Checking transformer, power supply and loop voltages
  • Measuring resistance of magnetic contacts and alarm loops
  • Checking for foreign grounds on any wiring

DMM’s come in a wide variety of price points and quality levels. Very cheap, lightly constructed units with basic measurement features are good enough for occasional use around the house.

A good example is the Cen-Tech 7 function digital multimeter sold by Harbor Freight. It can cost under $10 when on sale, and is even offered for free with the purchase of occasional promo items.

If you’re a do-it-yourselfer, better quality meters will have more features and sturdier construction. The Extech MN35 Digital Mini Multimeter falls into this category, and only costs around $25 from many online sources.

For alarm professionals and serious DIYers, a high-quality handheld multimeter is a good investment. Fluke digital multimeters are among the very best, along with brands like B&K, Beckman Industrial, Gardner Bender, and a few others. A good Fluke digital multimeter can cost $200 or more, depending on features, but it will probably last you for life.

Higher-quality DMM’s will usually have many of these useful features:

  • “Autoranging”, which automatically selects the correct measurement range without having to do it manually.

  • A “Continuity Check” feature is nice, and provides an audible beep when a circuit is closed.

  • Capacitance tester

  • Diode tester

  • Transistor tester

  • Max/Min Function records the highest and lowest readings that occur during a sampling period. The period starts when you activate the Min/Max function, and ends when you clear the function.This is most handy when tracking down intermittent opens or grounds on an alarm loop.

If you’re an alarm professional, or plan on becoming one, I recommend getting the best DMM you can afford with the features you’ll use. Good quality meters are built to last, and many have a rubberized case that may save the day (or days!) when you accidentally drop the unit from a ladder to a concrete floor. (Don’t ask me how I know about this…:-))

I have used the same Beckman Industrial Autoranging Digital Multimeter, a model RMS225, for decades. It has MAX/MIN and HOLD features to temporarily store readings, and a diode test function that I’ve used occasionally.

Priced around $180 when I bought it, this DMM was actually a better meter than I needed at the time. Over the years though, I’m glad I got a tool with the features and tough construction this one has. It sure wasn’t cheap, but it has withstood a ton of rough handling and has never failed to work flawlessly.

Beckman Industrial RMS225

If you are a home do-it-yourselfer, there are many decent DMMs available at reasonable prices. These probably won’t survive as much ‘medieval’ handling as the more expensive units. But, if they break, they’re much cheaper to replace.

Standard digital multimeter test leads on left, upgraded leads with alligator clip attachments on right

Tech Tip: Consider Upgrading to More Useful Test Leads

The “stock” test leads included with most standard digital multimeters are of decent quality, but they are usually just plain test probes.

Depending on how you use your meter and what you need to measure, other options may make your work quite a bit easier.

For alarm service use, I upgraded the factory test leads that came with my Beckman Industrial Model RMS225. I bought a set of aftermarket test leads with various screw-on attachments to make some common tasks easier. These are very well made, and include several different specialty tips that come in handy.

Alligator clip screw-on attachments removed

The most useful of these to me are the alligator clips tips, which allow you to make quick connections to battery terminals, alarm panel screws, or bare wires simply by clamping on the alligator clips.

This greatly simplifies the testing of batteries, or the reading of a varying voltage or resistance, without having to manually hold the test probes against the terminals being tested.

When you need regular test probes, just remove the alligator clips. Or, you can screw on a different accessory attachment. This test lead kit came with adapters for ring terminals, banana plugs, micro-clips, and of course, alligator clips.

These clips are especially helpful when troubleshooting intermittent switches. Just connect the clips to the switch wires, then use the Max/Min feature to record what happens when you move to the problem switch to spray chiller or rap on it.

You can learn tips on how to use a multimeter by reading some of my pages covering specific troubleshooting problems, as well as any of the many multimeter tutorials available elsewhere on the web.

See how to use a digital multimeter for testing an alarm system battery.

Related Articles:

Wire Stripper Tools, Cutters, and Crimpers

The All in One Screwdriver and Other Useful Screwdrivers

Using a Tone and Probe Kit for Finding Cut Alarm Wires

Using a Continuity Tester for Alarm Installation and Service

MagLite LED Flashlight and Other Small Flashlights

Electrician Tool Pouch And Other Tool Bags and Buckets

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