TRJ 2 PCS Thermostat Lock Box with Key, Large Thermostat Cover with Lock for Thermostat on Wall, AC Control Lock Box Cover with Key, Air Conditioner Lockbox Fits Thermostats 5" H x 6" W or Smaller

Why I picked up this thermostat lock box

In shared spaces, someone always finds the thermostat. In my case, it was a busy café where staff and customers took turns nudging the temperature up and down. I needed a simple way to keep settings consistent without upgrading to a networked control system. That’s what led me to try the TRJ thermostat lock box, a clear, lockable cover designed to keep hands off while still letting the thermostat do its job.

I installed the two-pack—one in the café and one in a small rental hallway where tenants tend to bump the setpoint. After a few weeks of use, here’s how it held up.

Build quality and design

The cover is made from clear polycarbonate (PC), which is a good choice for this kind of product: it’s tough, resists chemicals, and is less prone to yellowing under UV exposure than cheaper acrylics. The clarity is excellent. From normal viewing distance, I can read the thermostat display without opening the cover. The edges are cleanly molded and the overall finish is better than I expected at this price point.

Ventilation cutouts run along all four sides. With some covers, ventilation is more of a marketing checkbox than a working feature, but here the slots are generous enough that they actually allow air to circulate around the thermostat. That matters because a sealed box can trap heat and skew readings. In both installations, I didn’t see any measurable impact on temperature sensing.

The lock is a simple cam lock actuated by a key. It’s not a high-security mechanism, but it’s perfectly fine for what this product is supposed to do—stop casual tampering. The door aligns well with the frame, and the lock has a positive feel when it engages. There’s a little bit of flex in the door if you push at the center, which is typical of thin PC panels, but once locked it sits snugly.

Aesthetically, it’s unobtrusive. The clear design blends into painted walls better than an opaque cage or metal guard. It reads as “professional” without looking industrial.

Fit and compatibility: measure depth carefully

TRJ lists compatibility for thermostats up to roughly 7 inches wide, 4.7 inches high, and about 2 inches deep. On my sample, the internal clearance measured close to 7.0" W x 4.7" H x 2.0" D. That last number—depth—is the one to watch. If your thermostat or its trim plate stands proud of the wall, or if the wiring bundle causes the unit to sit forward, you can run out of space quickly.

A few fit notes from my installs:
- A standard, rectangular programmable thermostat fit with comfortable clearance.
- A chubbier touchscreen model fit on width and height but left only a few millimeters of space at the front; still fine, but no room to spare.
- Decorative trim plates can be the deal-breaker. One of my thermostats had a cosmetic backplate that added thickness; I removed it to make the lock box close smoothly.

Plan for the full footprint, not just the thermostat body. Measure width, height, and protrusion from the wall—front bezel included.

Installation: straightforward with a couple of caveats

Installation is simple and doesn’t require removing the thermostat. I used a drill, a screwdriver, a small level, and a pencil.

Steps that worked well:
1. Hold the backplate over the thermostat and mark the mounting holes.
2. Confirm that the door will clear the thermostat when closed; adjust position if your unit sits toward one side.
3. If your thermostat uses replaceable batteries with a front door, consider mounting the lock box slightly off-center so you can still open the battery compartment without removing the cover. A few millimeters can make all the difference.
4. Use appropriate wall anchors for drywall or masonry. Don’t overtighten—polycarbonate is durable, but you can deform the backplate if you crank down too hard.
5. Attach the cover, lock it, and verify that the lock cam engages fully without rubbing on the thermostat.

Both of my installations took under 15 minutes each. The only fiddly moment was aligning the box so the thermostat sat centered and the door closed without touching the faceplate. Once it’s mounted, it feels secure and tidy.

Day-to-day use and performance

In daily operation, the lock box has been transparent—literally and functionally. Staff can still see the setpoint and system status from outside the cover, and I can unlock it to make seasonal adjustments. The ventilation works; my café thermostat didn’t overcompensate or drift as I’ve seen with less breathable covers. There’s no fogging or condensation.

The polycarbonate has held up to fingerprints and disinfectant wipes without clouding. It also doesn’t rattle, and the hinge (on my units) opens and closes smoothly. I’ve bumped the cover a few times while cleaning and it shows no signs of cracking or stress.

Security: deterrence done right

This is not a safe—it’s a deterrent. And as a deterrent, it’s effective. It completely stopped opportunistic fiddling in both locations. The simple lock is enough to keep hands off and to signal that the thermostat is off-limits.

Could someone determined get through with tools? Sure. But that’s not the target threat model for a product like this. The balance of visibility, convenience, and basic tamper resistance feels right. Because it’s clear, it doesn’t invite curiosity; people can see the settings, so it doesn’t feel like something “hidden” behind a cover.

Maintenance and usability tips

A few small practices helped:
- Keep a spare key with the facility keys. The lock feels robust, but a misplaced key will turn an easy adjustment into a hassle.
- If your thermostat uses batteries, the off-center mounting trick makes replacements painless.
- Clean with mild soap and water or a plastic-safe cleaner; avoid ammonia-based sprays that can haze plastics over time.

Value and use cases

As a two-pack, the value is strong if you have multiple thermostats or mixed-use spaces. For small businesses, community rooms, schools, and rental common areas, it’s an easy win. It also works at home if you have kids who love buttons or housemates with competing temperature preferences.

Compared with software-based locks on smart thermostats, this physical cover has a different advantage: it works for virtually any conventional wall unit and doesn’t require accounts, permissions, or app literacy. If someone manually presses buttons, the cover ends the debate.

What could be better

There are two areas to watch:
- Depth tolerance: With an internal depth around 2 inches on my unit, some bulkier thermostats and trim plates won’t fit cleanly. If TRJ offered a slightly deeper version (say, 2.5 inches), it would cover more scenarios.
- Lock standardization: The included keyed lock works, but keyed-alike options or a simple master key system would be useful for multi-site managers.

None of these are deal-breakers for typical commercial thermostats, but if you’re running a large smart thermostat with a pronounced face or a thick decorative plate, measure carefully or consider a deeper enclosure.

Who it’s for

• Small businesses that need consistent temperature control without staff overrides.
• Landlords managing common areas.
• Schools, churches, and community spaces with frequent public access.
• Homes where the thermostat needs to be visible but off-limits.

If your thermostats are slim and rectangular, you’re in the sweet spot. If they’re oversized or paired with thick trim, you may need a different enclosure.

Final recommendation

I recommend the TRJ thermostat lock box. It’s clear, durable, and easy to install without touching the thermostat wiring. The four-sided ventilation preserves temperature accuracy, and the simple keyed lock is enough to stop casual tampering. Just measure your thermostat—including its protrusion from the wall—and be mindful of the roughly 2-inch internal depth. For most standard units in offices, shops, and common areas, this lock box is a practical, low-friction way to keep your settings where you want them.