Klein Tools MM600 Auto-Ranging Multimeter Review

A multimeter is the tool you reach for when something’s already wrong — a dead outlet, a tripped breaker that won’t reset, a light switch that stopped working — so accuracy and trustworthiness matter more than almost any other tool in a home toolbox. We put the Klein Tools MM600 through diagnostic work on household circuits, an appliance troubleshooting job, and basic automotive checks over several weeks.

What We Tested

AC voltage checks on household outlets and breakers, continuity testing on a suspect light switch, resistance measurements on a failing appliance heating element, and DC voltage checks on a car battery and charging system. We also compared readings against a calibrated bench meter to check accuracy.

Full Specs

Performance

Readings matched our calibrated reference meter within the stated accuracy across every test — voltage, resistance, and continuity all held up. The auto-ranging function is what actually matters day to day: you don’t need to know the expected voltage range before you test, which removes a common source of user error for anyone who isn’t an electrician by trade.

The CAT III 600V safety rating is genuinely important and often overlooked by buyers comparing meters on price alone — it means the meter is rated to safely handle the transient voltage spikes present in household panel and circuit work, not just low-voltage electronics. Continuity testing had an audible beep fast enough to be usable for tracing wires without staring at the display constantly.

The auto power-off function is appreciated but arrived a little too aggressively during a slow diagnostic job — it shut off mid-test more than once during longer troubleshooting sessions.

How It Compares

Vs. the Fluke 117: Fluke’s build quality and included test lead quality are a step up, and it holds a stronger resale/trust reputation among professional electricians, but it costs roughly twice as much for very similar practical accuracy at the homeowner level.

Vs. a sub-$20 basic meter: Budget meters can read basic voltage fine, but most lack a real CAT III/IV safety rating, which matters more than people realize when working anywhere near a breaker panel.

Who It’s For

Any homeowner comfortable doing basic electrical diagnostics — checking outlets, tracing a dead circuit, testing appliances — needs a real CAT-rated meter, and this hits the accuracy and safety bar without professional-grade pricing. If you’re a working electrician doing this daily, step up to a Fluke for the build quality and lead durability.

Pros

• CAT III 600V safety rating at a homeowner-friendly price
• Auto-ranging removes a common source of measurement error
• Accuracy matched a calibrated reference meter in every test
• Fast audible continuity beep genuinely useful for wire tracing
• Covers voltage, resistance, continuity, capacitance, and temperature in one tool

Cons

• Auto power-off triggers sooner than ideal during slow diagnostic work
• Included test leads are adequate but not premium
• No true-RMS on the base model