Choosing the right 4-gas monitor for a crew is a procurement decision, not a product-review exercise. At PK Safety, we've been fitting industrial and emergency-response teams with gas detection since 1984, and we frequently get asked: which 4-gas monitor should my team actually carry? This guide names the six models we recommend most often for crew-scale buying, explains who each one is for in one line, and tells you how to match the pick to the hazard. Every monitor in the list is one PK Safety stocks, calibrates, and services in-house, so your service relationship doesn't end at the sale.
The six picks below are the models we hand to safety managers, confined-space supervisors, and operations leads most often. A compliant 4-gas monitor is one your crew will actually wear every shift and that your calibration workflow can keep in spec; the right pick depends on fleet size, hazard profile, and whether you want to service or replace. The decision helper near the end translates the six picks into a short "what to buy for which job" chart.
The six monitors at a glance
| Monitor | Best for | Serviceable or disposable | Sampling type | Warranty tier |
|---|---|---|---|---|
| RKI GX-3R | Compact confined-space wear | Serviceable | Diffusion | 3-year |
| BW MicroClip XL | Fleet default | Serviceable | Diffusion | 2-year |
| BW GasAlertMax XT II | Pre-entry pumped sampling | Serviceable | Pumped (integrated) | 2-year |
| BW Clip4 | Disposable fleet | Disposable | Diffusion | 2-year, non-rechargeable |
| WatchGas SST4-MICRO | Serviceable premium | Serviceable | Diffusion | 2-year |
| MSA Altair 4XR | MSA-standardized sites | Serviceable | Diffusion | 4-year |
Monitor-by-monitor breakdown
RKI GX-3R: the compact anchor
Who it's for: confined-space entry teams that need a small, pocketable monitor every crew member will actually wear every shift.
The RKI GX-3R 4-gas monitor is the smallest intrinsically safe 4-gas we stock, backed by a 3-year warranty. It covers O₂, LEL (combustibles, calibrated for methane as the reference LEL gas), CO, and H₂S in a unit that fits a shirt pocket and clips to a lapel. It is approved for Class I Division 1 Groups A–D T4 by CSA, carries ATEX II 1 G marking, and holds IECEx certification — the full set of hazardous-location approvals your permit-required confined space program will ask for. In the field we see it most often with municipal utility crews, oil and gas service companies, and emergency-response teams that need something small enough to wear through a 10-hour shift without being set aside.
PK Safety is RKI Instruments' #1 distributor, with in-house RKI technicians on staff. If a GX-3R needs calibration, sensor replacement, or warranty service, it stays in our building.
BW MicroClip XL: the fleet default
Who it's for: operations buying ten or more units where total cost of ownership and simplicity beat feature count.
The BW MicroClip XL is the model you see on more industrial job sites than any other 4-gas we sell. It runs diffusion sampling, covers the same O₂ / LEL / CO / H₂S set, and carries a two-year factory warranty. Unlike disposable monitors, it’s fully serviceable: when a sensor reaches end of life, you replace that sensor instead of the whole unit. For procurement teams spec’ing a fleet, that’s the point. You buy the monitor once, bump-test it before every shift, calibrate it every six months, and swap sensors only as needed, so the unit stays in service well beyond the warranty period. PK Safety is a Factory Authorized Honeywell/BW Service Center, so service and sensor replacement go through us directly rather than back to the manufacturer.
BW GasAlertMax XT II: the pumped option
Who it's for: confined-space entry supervisors who need to pre-test a vessel or vault before anyone drops a line.
Pre-entry atmospheric testing is a different job from routine wear during work, and the BW GasAlertMax XT II is the model we hand entry supervisors who need to draw a sample from several feet away. The integrated sampling pump runs on battery power, so there is no separate hand-aspirator pump to carry. The same O₂ / LEL / CO / H₂S coverage applies. For teams that run both pre-entry testing and in-space wear, we often spec a GasAlertMax XT II for the supervisor and MicroClip XLs for the crew — one pumped monitor outside, diffusion monitors inside.
BW Clip4: the disposable workhorse
Who it's for: fleets that would rather replace than service, and short-term contractors who need compliance coverage for a single job.
The BW Clip4 is a 4-gas maintenance-free detector providing two full years of continuous operation: no charging, no battery changes, no sensors to replace. At the end of two years it retires, and you buy another one. For contractors mobilizing to a job for a few weeks and short-staffed safety programs that don't want to run a calibration workflow, the Clip4 removes the maintenance variable entirely. We also see it as a backup unit at facilities that otherwise standardize on serviceable monitors — kept in a drawer for the day someone's primary monitor fails a bump test.
WatchGas SST4-MICRO: the phone-connected pick
Who it's for: fleets that want to configure, bump test, and pull data from their monitors with a phone instead of a laptop.
The WatchGas SST4-MICRO connects to your phone with a tap. The free WatchGas SST app (iOS and Android) uses NFC, so there's no cable and no laptop. Hold the monitor to an NFC-capable phone and you can download gas event logs, change settings, and assign the unit to a worker. Bump testing and calibration can be done manually or run through the SST Dock (sold separately) and the same app. Charging is by induction, so there are no charge contacts to wear out.
A supervisor handing out monitors to a mixed crew can tap each one to confirm its configuration before it leaves the shop. Field-swappable sensors, unusual at the compact end, mean you replace a sensor instead of retiring the monitor. WatchGas is a newer brand for us and PK Safety now services the full WatchGas SST monitor line with factory-trained technicians in-house.
MSA Altair 4XR: the MSA-standardized pick
Who it's for: buyers at MSA-standardized sites who need a brand match for an existing fleet.
Many large industrial accounts standardize on MSA across their safety program, and the MSA Altair 4XR is the 4-gas model that lands in those fleets. It covers the same O₂ / LEL / CO / H₂S set, runs on a rechargeable battery, and integrates with MSA's docking and data management ecosystem. If your facility already runs Altair detectors elsewhere — single-gas, portable area, or fixed — the 4XR keeps your fleet brand-consistent and your docking stations compatible.
How to choose: match the monitor to the hazard
Six models is more than most buyers want to think about at once. These four questions narrow the field in under a minute:
- Are you pre-testing a confined space before entry? BW GasAlertMax XT II (pumped). Diffusion monitors are designed to be worn, not to draw a sample from a distance.
- Are you spec'ing the standard-issue monitor for a fleet of 10+? BW MicroClip XL or RKI GX-3R. Both are diffusion, both are compact, both are the default picks for in-space wear.
- Would you rather replace than service? BW Clip4. No calibration, no sensor swaps, retire-and-replace at two years.
- Do you already have a calibration workflow and want to extend unit life? WatchGas SST4-MICRO or RKI GX-3R. Both are serviceable; both let you swap sensors instead of retiring the unit.
- Do you know what specific combustibles are being detected? In general, low power LEL IR sensors in the BW Clip4 and WatchGas SST4-Micro have great battery life and are immune to poisons, but they cannot detect Hydrogen or Acetylene. Conventional CAT-Bead sensors in the BW Microclips, BW MAX XT II , RKI GX-3R, and MSA Altair have a wide range of detection but can be prone to sensor poisoning and inhibition.
Brand standardization is a legitimate fifth variable. If your site is already MSA across the rest of the safety program, the Altair 4XR keeps your docking and data pipelines consistent.
Service, calibration, and support
PK Safety has been in gas detection since 1947. We are RKI Instruments' #1 distributor for the past two years, a Factory Authorized Service Center for BW, RKI, WatchGas and RAE, and we keep in-house technicians trained on these gas monitors. When you buy a monitor from us, calibration, bump-test gas, replacement sensors, and warranty service all stay in one shop. That matters more than most spec sheets admit: a monitor that cannot be serviced gets set aside the first time it fails a bump test.
For a quote, a mixed-fleet procurement call, or help spec'ing a brand swap, reach our gas detection experts at 800.829.9580. Our gas monitor calibration and repair technicians can offer their expertise and support even if you haven't bought your gas detection devices from us.
Photo credit: WatchGas
Frequently Asked Questions
What does a 4-gas monitor detect?
A 4-gas monitor measures the four atmospheric hazards OSHA's permit-required confined space standard (29 CFR 1910.146) requires monitoring for before and during entry: oxygen (O₂), lower explosive limit (LEL, measured as a percentage of the lowest flammable concentration — most monitors are factory-calibrated for methane as the reference gas), carbon monoxide (CO), and hydrogen sulfide (H₂S). O₂ reads a deficiency or an enriched atmosphere, LEL reads approaching combustibility, CO reads the toxic byproduct of incomplete combustion, and H₂S reads the toxic gas common in oil and gas, wastewater, and decomposing organic environments.
How do I choose between a diffusion monitor and a pumped monitor?
Diffusion monitors are worn on the body and sample the atmosphere continuously while the user works in the space. Pumped monitors draw a sample from a distance, which is what you want for pre-entry testing of a vessel, vault, or manhole before anyone enters. In our range the BW GasAlertMax XT II is the pumped pick for pre-entry supervisors. The RKI GX-3R, BW MicroClip XL, BW Clip4, WatchGas SST4-MICRO, and MSA Altair 4XR are diffusion monitors for in-space wear. Many entry teams spec one pumped monitor for the supervisor and diffusion monitors for the crew.
Should I buy serviceable or disposable monitors for a fleet?
It is a trade-off. Serviceable monitors (RKI GX-3R, WatchGas SST4-MICRO, MSA Altair 4XR) have a lower lifetime cost per unit if your team swaps sensors and sends units in for scheduled calibration. Disposable monitors (BW Clip4) require no charging, no battery changes, no sensor replacements and have a predictable cost per year — you replace the whole unit at the two-year mark. Fleets that already run a calibration workflow lean serviceable. Fleets without that infrastructure, or short-term contractors who need compliance coverage for a single job, lean disposable.
How often does a 4-gas monitor need to be calibrated?
Perform a bump test before every shift — OSHA's Safety and Health Information Bulletin 09-30-13 recognizes bump testing as the acceptable daily verification. Perform a full calibration every six months at minimum, or whenever a monitor fails a bump test. PK Safety operates a gas monitor calibration and repair depot that handles RKI, BW/Honeywell, MSA, and WatchGas monitors on a flat-rate per-monitor basis.
What is the 10% LEL action threshold?
10% of the Lower Explosive Limit is the action threshold OSHA references in the preamble to 29 CFR 1910.146 for permit-required confined spaces. In practice, most entry programs trigger an alarm and begin corrective ventilation at or above 10% LEL, trigger evacuation at 25% LEL, and require below 1% LEL for continued entry. A 4-gas monitor's LEL channel is factory-calibrated against methane; readings for other combustibles will differ by a known correction factor documented in the monitor's manual.
Can I mix brands in one fleet?
Yes. PK Safety stocks and services RKI, BW/Honeywell, MSA, and WatchGas, which is why procurement teams at mixed-fleet sites consolidate their gas detection ordering here. One purchase order, one service relationship, one calibration shop. If you are standardizing on a single brand but keeping a few legacy units from a previous spec, we can calibrate and service both.