Best Combustible Gas Leak Detectors: ET120 vs GSD600

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Choose the Klein ET120 for two sensitivity modes and AAA power; choose the Amprobe GSD600 if an earphone connection matters. Both are handheld locating tools for planned qualified work. Their LEDs indicate a response, not a numeric concentration or an all-clear. Neither replaces an installed alarm, a required pressure test or a qualified gas repair.

If you smell gas or suspect an emergency leak, leave first. National Fuel advises leaving even for a slight odor, then calling the gas utility or 911 from a safe place. Do not use a phone inside, operate switches or appliances, smoke or light anything. Do not delay leaving to search with a detector. This comparison is for choosing a tool for planned work by a qualified installer.

A combustible gas leak detector is a sniffer: a gas sensor on a flexible probe that beeps faster and lights more LEDs as it gets closer to methane or propane. It helps a qualified installer find which joint is leaking during planned work, such as after a pressure test fails to hold. Its lights are a rough signal, not a calibrated gas reading; it does not tell you a system is safe, and it does not measure pressure.

Klein ET120 vs Amprobe GSD600 at a Glance

Neither detector shows a numeric ppm measurement or identifies which gas is present. Dark LEDs do not prove that gas is absent. Klein’s public documents disagree on the ET120’s sensor, alarm loudness, dimensions and some controls. We cannot confirm the hardware revision shipped under this listing, so we do not rank either tool by those disputed fields. Follow the manual supplied with your exact unit.

Gas indication, power and package differences
Check	Klein Tools ET120	Amprobe GSD600
Gases named by the maker	Methane, propane and butane (manual)	Methane and propane
Rated range (maker)	50 to 10,000 ppm, based on methane; other gases read differently	Methane 40 to 640 ppm; propane 35 to 580 ppm
Sensitivity modes	HIGH 50 to 1,000 ppm; LOW 1,000 to 10,000 ppm	Five-level LED indication marked for methane/propane; no gas identification or numeric concentration readout.
Start-up	50-second zero in clean air	Warm-up under 60 seconds in clean air
Response	3 seconds after zero	Under 10 seconds; at least 2 minutes to recover after a leak
Probe	18 in. gooseneck	17.6 in. flexible probe
Power	4 AAA (included)	4 AA; optional 9 V adaptor not included
Alarm	Ticking tone and 5 red LEDs; mute button	Beep rate and LEDs; mute switch; earphone jack (earphone not included)
Operating temperature	32 to 122°F	23 to 113°F
In the box	Detector, 4 AAA batteries, manual, storage pouch	Detector and batteries; see the box note below
Warranty	Product-group/packaging terms; proof of authorized-distributor purchase. See conditions below.	1 year from purchase under model-manual conditions; batteries and specified damage excluded.

How to Choose

Indication range. Klein specifies HIGH at approximately 50–1,000 ppm and LOW at 1,000–10,000 ppm, based on methane. Amprobe specifies 40–640 ppm methane and 35–580 ppm propane. These different response ranges help compare tools; they do not establish a safe atmosphere or authorize continued searching during a suspected emergency.
Gas scope. Both makers name methane and propane. Amprobe publishes different response ranges for those gases; its marked five-level indicator does not tell you which gas or mixture is present. Do not compare its propane threshold with Klein’s methane-based range as if they were the same sensitivity test.
Batteries. The ET120 runs on 4 AAA, included. The GSD600 runs on 4 AA, or a 9 V adaptor you buy separately; Amprobe rates the batteries at 14 hours of continuous use.
Noise. In a loud mechanical room, the GSD600’s earphone jack lets you hear the beep through a standard earphone.
Start in clean air. Both makers say to turn the detector on where there is no gas. Klein warns that zeroing in gas gives lower-than-actual readings, and gas may go undetected.

Two sensitivity modes, AAA power

Klein Tools ET120 Combustible Gas Leak Detector

50 to 10,000 ppm (methane) · HIGH 50 to 1,000 / LOW 1,000 to 10,000 ppm · 50-second zero · 3-second response · 18 in. gooseneck · 4 AAA included · 5 to 7 year sensor life expectancy · 32 to 122°F · 2 m maker drop-protection reference · 1/4-20 tripod mount

The ET120 offers HIGH and LOW sensitivity modes, visual LEDs, a ticking alert, HOLD and zero controls. Klein lists a five-to-seven-year sensor life expectancy, not a guarantee that an aged or damaged sensor remains usable. Its manual versions differ on Zero-button and sensor-failure behavior; follow the manual supplied with your unit. Stop using a failed detector, and do not attempt internal repairs: Klein lists no user-serviceable parts.

Widest range here, with two sensitivity modes
AAA batteries and a pouch in the box
Sensor-failure alert and HOLD button

Not insulated: Klein says to shut off power before probing near live parts
Do not change batteries in an explosive atmosphere
Sensor is not user-replaceable

Choose it if you want the two sensitivity modes and AAA power for planned qualified locating work. Choose the GSD600 instead if an earphone connection is important. Neither provides gas identification or an all-clear.

Check the Klein ET120 on Amazon

Earphone connection, AA power

Amprobe GSD600 Gas Leak Detector

Methane 40 to 640 ppm · propane 35 to 580 ppm · 5-level LEDs (above 40, 80, 160, 320 and 640 ppm) · warm-up under 60 seconds · response under 10 seconds · 17.6 in. probe · 4 AA, about 14 hours continuous · earphone jack and mute switch · 23 to 113°F · 1-year warranty

The GSD600 calibrates itself at power-up and uses a READY indicator after warm-up. Its manual specifies at least two minutes for sensor recovery after detection. It warns that silicone vapor can coat the sensor and reduce effectiveness, while water can change its response. These maintenance limits matter when choosing a tool; they are not gas-repair instructions.

What is in the box: Amprobe’s product page lists the GSD600, an installed battery and a carrying case. Its users manual lists the GSD600, 4 AA batteries and the manual, with no case. Expect the detector and batteries; do not count on the case.

Documented methane and propane response ranges
Earphone jack for loud rooms
Optional 9 V adaptor input

Narrow range: all methane LEDs are lit above 640 ppm
Two-minute recovery after a hit
Earphone and adaptor sold separately

Choose it when you want an earphone connection and are prepared to supply the earphone separately. Choose the ET120 if its two sensitivity modes or AAA batteries better suit your planned work. The GSD600’s LEDs are not a gas identifier or a numeric ppm measurement.

Check the Amprobe GSD600 on Amazon

Not Linked: UEi CD100A

UEi CD100A was excluded from the October 7 shortlist because its checked offer was a third-party seller. It is not an approved purchase here. This comparison links only the two qualified exact models above.

Before buying: tool limits and upkeep

Match the job. These are handheld combustible-gas locating tools. If you need an installed gas alarm, a CO alarm or meter, or a pressure-test gauge, choose the appropriate equipment instead. Our gas pressure test gauge guide covers the last of these.
Allow for clean-air start-up. Klein specifies a 50-second zero; Amprobe specifies a warm-up of less than 60 seconds. Klein warns that zeroing in gas can produce lower readings and missed gas. Amprobe calls for at least two minutes of recovery after detection; a depleted or contaminated sensor is not a reliable shortcut.
Check the work environment. Klein lists 32–122°F operation; Amprobe lists 23–113°F. Klein warns that the ET120 is not insulated and forbids battery replacement in an explosive atmosphere. Amprobe warns against low-oxygen operation and sensor exposure to silicone vapor, corrosive materials or water. Read the manual supplied with the exact unit and leave gas work to a qualified installer.
Plan the extras. Klein’s page lists four AAA batteries and a pouch. Amprobe lists AA power; its optional 9 V adapter and earphone are not included. The Amprobe product page/datasheet list a case while its manual’s accessory list omits one, so confirm that package if a case matters.
Keep the receipt and read the warranty conditions. Amprobe’s model manual states one year from purchase for material/workmanship defects, with proof of purchase and exclusions for disposable batteries, contamination, misuse and other listed damage. Klein’s current manual refers to its product-group policy: packaging can change the stated period, batteries/wear/misuse are excluded, and claims require proof of purchase from an authorized distributor. Do not substitute Klein’s hand-tool lifetime terms for this detector.

FAQ

What should I do if I smell gas?

Leave first. National Fuel, a gas utility, says to get out, then call the utility or 911 from a safe place, and not to use a phone, light anything or operate switches or appliances inside. Do not use a leak detector to search for the source.

Can I use either detector as a carbon monoxide alarm or meter?

No. Klein describes the ET120 for combustible gases and Amprobe describes the GSD600 for methane and propane. Do not use either as a CO alarm or as proof that carbon monoxide is absent; choose equipment specifically intended for CO.

Does a gas leak detector replace a pressure test?

No. Klein says the ET120 is not intended to prove the absence or concentration of combustible gases. A locating tool and a pressure test serve different purposes. A qualified installer must follow the applicable test and inspection requirements; neither a quiet detector nor this guide certifies a line as gas-tight.

Can vapors or contamination affect a detector?

Amprobe warns that silicone vapor can coat its sensor, and water, corrosive materials or prolonged high-gas exposure can damage it or change its response. A suspected gas alarm should not be dismissed as cleaner or glue. Leave and contact the utility during a suspected emergency; sensor assessment and planned work require the maker instructions and qualified help.

What batteries do these detectors use?

The Klein ET120 uses 4 AAA batteries, included. The Amprobe GSD600 uses 4 AA batteries or an optional 9 V adaptor that is not included.

Why Trust Plumbing Picks

Plumbing Picks is written by a licensed Georgia journeyman plumber. This comparison uses the linked maker documents and published package information, not hands-on testing. We checked the two exact Amazon offers on October 7, 2026 at approximately 12:40–12:41 PM Eastern: both were New, in stock and sold by Amazon.com. Stock, seller and supplied hardware can change. Nobody pays to be included here. See who writes this and how we pick.

Sources

Which detector should you choose?

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Choose the ET120 for its two methane-based sensitivity ranges, AAA power and listed pouch. Choose the GSD600 if an earphone connection matters, allowing for AA batteries, recovery time and any extras. Choose neither if you need an installed alarm, CO measurement, gas identification, an all-clear or a substitute for qualified gas work.