7 Best Thermostat Lock Boxes and Guards (October 2026)

The best thermostat lock boxes and guards include the Honeywell Home Large Thermostat Guard CG512A1009 for larger thermostats, the Honeywell Home Medium Thermostat Guard CG511A1000 for medium-size Honeywell controls, and the TRJ Thermostat Lock Box with Key for a clear, ventilated cover.

On this page (6 sections)

1. How we compared thermostat lock boxes
2. The best thermostat lock boxes and guards
3. What should you measure before buying a thermostat guard?
4. Is a keyed or combination thermostat lock box better?
5. Does a thermostat lock box affect temperature sensing?
6. Final choice: which thermostat lock box should you pick?

The best thermostat lock box for most larger controls is the Honeywell Home Large Thermostat Guard CG512A1009, with a key lock and a stated fit for thermostats up to 8.25 in wide. The medium Honeywell guard fits smaller controls, while Pihode offers a combination lock if you want keyless access.

A lock box can help prevent children, tenants or visitors from changing a thermostat setting. Choose based on the thermostat's size, the lock style you prefer and the available wall space.

If you haven't chosen a thermostat yet, compare options in our guide to thermostats for your home. For installation questions, see our thermostat fit and installation guide.

Our picks at a glance

1. 1
   Best for larger thermostats

   Honeywell Home Large Thermostat Guard CG512A1009

   8.4/10 our score

   See it on Amazon
2. 2
   Best for medium-size Honeywell controls

   Honeywell Home Medium Thermostat Guard CG511A1000

   8.2/10 our score

   See it on Amazon
3. 3
   Best for a clear, ventilated cover

   TRJ Thermostat Lock Box with Key

   7.8/10 our score

   See it on Amazon

4. 4

   Gedreew Large Thermostat Lock Box

   Best for a deeper thermostat
   Check it
5. 5

   Pihode Combination Thermostat Lock Box

   Best for keyless access
   Check it
6. 6

   JGWPA Universal Thermostat Lock Box

   Best for two mounting options
   Check it
7. 7

   GYFVBH Large Thermostat Lock Box

   Best for a compact thermostat
   Check it

How we compared thermostat lock boxes

The best thermostat guard is the one that fits your control and matches how you want to manage access. We compared fit dimensions, lock type, material and installation features, then scored each pick for this use.

Our score weighs specs, features and buyer feedback against what you're shopping for. Scores reflect fit and useful features for limiting access.

A lock box needs enough room around the thermostat without blocking access to doors or nearby controls. Check the thermostat's full width, height and depth, including projecting buttons or trim.

The best thermostat lock boxes and guards

These thermostat lock boxes are ordered from highest score to lowest. Start with the fit dimensions, then compare lock style and mounting approach.

1

Honeywell Home Large Thermostat Guard CG512A1009: Best for larger thermostats

8.4/10Our score

• Fits thermostats up to 8.25 in W x 5.75 in H x 2.75 in D
• Key lock with inner shelf
• Clear acrylic resin cover and base
• Wall mount

The largest stated fit in this group suits a wide thermostat or a control that needs more room. Its inner shelf and key lock help limit access to the settings.

See it on Amazon

Pros

• Largest stated thermostat fit here
• Key lock and inner shelf
• Clear cover resists yellowing

Cons

• Requires wall mounting
• Some Honeywell models need off-center mounting for battery-door access

The Honeywell Home Large Thermostat Guard CG512A1009 is the top pick for a thermostat that needs a wider cover. Its maximum thermostat fit is 8.25 in W x 5.75 in H x 2.75 in D, the largest width in this group.

The clear acrylic resin cover and base resist yellowing from chemicals and UV light. A key lock and inner shelf help limit access to heating and cooling settings while leaving the thermostat visible.

This guard mounts to the wall and includes mounting hardware. Some Honeywell models need off-center placement so the battery door can open, so check for clearance before installation.

Choose it for a wide thermostat or a control that doesn't fit the medium guard. If your thermostat is smaller, the Honeywell Home medium guard has a more compact fit.

2

Honeywell Home Medium Thermostat Guard CG511A1000: Best for medium-size Honeywell controls

8.2/10Our score

• Fits thermostats up to 6 1/16 in W x 5 1/16 in H x 2 5/8 in D
• Key lock with inner shelf
• Clear plastic casing resists yellowing
• Wall mount

This medium guard fits several Honeywell thermostat families and other controls within its stated dimensions. Choose it when the large model would take up more wall space than needed.

See it on Amazon

Pros

• Fits several named Honeywell families
• Key lock and inner shelf
• Clear casing resists yellowing

Cons

• Smaller stated fit than the large guard
• Some thermostats may need a separate fit check

The Honeywell Home Medium Thermostat Guard CG511A1000 fits thermostats up to 6 1/16 in wide, 5 1/16 in high and 2 5/8 in deep. It fits several Honeywell families, including RTH8, RTH7, RTH6, RTH5 and CT3 models.

A key lock and inner shelf help prevent tampering. The clear plastic casing resists yellowing, and the guard mounts to the wall.

Check the thermostat dimensions against the maximum fit before choosing it. The guard itself measures 7.5 in wide, 6.5 in high and 3 in deep, so allow for the larger outside footprint.

Choose this Honeywell guard when the large model would take up more wall space than you need. For advice on changing or positioning a control, read about changing a thermostat and where to place a thermostat.

3

TRJ Thermostat Lock Box with Key: Best for a clear, ventilated cover

7.8/10Our score

• Fits devices up to 7 x 4.7 x 2.1 in
• Key lock
• Four-sided ventilation
• Polycarbonate cover

The TRJ guard combines a key lock with ventilation on four sides. Its stated size fits some wider controls, but check height and depth as well as width.

See it on Amazon

Pros

• Four-sided ventilation
• Key lock
• Can be installed without removing the thermostat

Cons

• Maximum height is 4.7 in
• Some models need off-center mounting for battery-door access

The TRJ Thermostat Lock Box with Key pairs a key lock with four-sided ventilation. It fits thermostats up to 7 in wide, 4.7 in high and 2.1 in deep.

The polycarbonate cover is described as chemically resistant, UV resistant and resistant to yellowing. It can be installed without removing the thermostat, though some models may need off-center placement to keep the battery door accessible.

Its height limit is shorter than the Honeywell guards, so measure carefully if your thermostat has a tall face or raised controls. The vents provide air paths around the thermostat.

Choose TRJ if you need a vented cover within its dimensions. For a deeper thermostat, compare the Gedreew large lock box.

4

Gedreew Large Thermostat Lock Box: Best for a deeper thermostat

7.6/10Our score

• Fits devices up to 7.28 x 5.75 x 2.75 in
• Key lock
• Four-sided ventilation
• Polycarbonate cover

The Gedreew guard allows more depth than several compact covers here. Its four-sided ventilation and key lock suit shared rooms where access should stay controlled.

See it on Amazon

Pros

• More stated depth than the TRJ and Pihode
• Four-sided ventilation
• Can be installed without removing the thermostat

Cons

• Measure the thermostat before choosing
• Some models need off-center mounting for battery-door access

The Gedreew Large Thermostat Lock Box fits devices up to 7.28 in W x 5.75 in H x 2.75 in D. Its stated depth is greater than the TRJ or Pihode limit.

Its polycarbonate cover has four-sided ventilation, and it can be installed without removing the thermostat. The key lock controls access, while the clear cover keeps the display in view.

The stated outer dimensions are 5.75 in wide, 5 in high and 2.75 in deep. Those dimensions differ from the maximum device fit, so check the box's measurements and available clearance carefully.

Choose it when you need more depth and a key lock. If sharing a numeric code would be easier than keeping a key, see the Pihode combination lock box.

5

Pihode Combination Thermostat Lock Box: Best for keyless access

7.4/10Our score

• Combination lock with settable code
• Fits devices up to 7.1 x 4.5 x 2.2 in
• Also fits sprinkler controllers within its size limit
• Vented polycarbonate cover

A settable combination code avoids managing a key and can be shared with family members. Its interior dimensions also limit the choice to shorter thermostats.

See it on Amazon

Pros

• Settable combination code
• Can also cover compatible sprinkler controllers
• Vented, transparent cover

Cons

• Shorter stated fit than the large guards
• No key lock

The Pihode Combination Thermostat Lock Box is the keyless pick in this roundup. You can set a numeric code and share it with family members who need access.

Its interior fits devices up to 7.1 in W x 4.5 in H x 2.2 in D. It also fits sprinkler controllers within those dimensions, and its transparent polycarbonate cover has air vents and rounded corners.

The shorter height limit is the main fit tradeoff. Measure the thermostat, including buttons or trim, and consider who will need the code.

Pick Pihode if avoiding a shared key matters more than fitting a taller control. If you prefer a keyed cover with two mounting options, the JGWPA has punch and nano-glue methods.

6

JGWPA Universal Thermostat Lock Box: Best for two mounting options

7.2/10Our score

• Inner size of 7 x 4.5 x 2 in
• Key lock with two keys
• Punch or nano-glue installation options
• Clear cover

The two stated mounting approaches give you a choice between screws and nano glue. Its usable depth is 2 in, so check that measurement closely.

See it on Amazon

Pros

• Two installation options
• Includes two keys
• Clear cover

Cons

• Shorter stated depth than several picks
• Nano-glue mounting may not suit every wall

The JGWPA Universal Thermostat Lock Box gives you a choice between punch mounting and nano glue. Its stated interior size is 7 in W x 4.5 in H x 2 in D, and it includes 2 keys.

That 2 in depth is the key measurement to check against your thermostat. The clear cover keeps the control visible, while the keyed lock helps restrict access to its settings.

JGWPA describes nano glue as a way to avoid damaging the wall. It may not suit every surface, so check the wall and installation instructions before choosing between glue and screws.

Choose this guard if you want mounting flexibility and your thermostat fits the shallow interior. For a more compact keyed option, compare the GYFVBH guard below.

7

GYFVBH Large Thermostat Lock Box: Best for a compact thermostat

6.9/10Our score

• Fits thermostats up to 6.3 x 4.72 x 2.2 in
• Key lock with included keys
• Open design for installation without thermostat removal
• Wall mount

This guard is aimed at smaller thermostats and offers a key lock. The maker also provides double-sided tape, though screw mounting is described as more secure.

See it on Amazon

Pros

• Key lock with included keys
• Open design for installation
• Tape or screw mounting

Cons

• Smaller usable width than the large guards
• Tape mounting is described as less secure

The GYFVBH Large Thermostat Lock Box fits thermostats up to 6.3 in W x 4.72 in H x 2.2 in D. Its open design allows installation without removing the thermostat, and it can be set horizontally or vertically.

It includes keys and can be mounted with screws or double-sided tape. The provided tape is described as less secure than screw installation, so choose based on the wall and how firmly the guard needs to stay in place.

The usable width is smaller than the Honeywell large guard and the TRJ or Gedreew covers. Measure first, especially if the thermostat has a broad frame around its display.

Choose it for a compact control and a keyed cover. If you need more room, compare the Honeywell large guard and its wider stated fit.

What should you measure before buying a thermostat guard?

Measure the thermostat's width, height and depth, then compare each number with the guard's maximum fit. Do not use the guard's outer dimensions as the available space.

Include raised buttons, side trim and any part that sticks out from the wall. If the thermostat has a battery door, check whether the cover or mounting position could block it.

A thermostat's location also matters. Our guide to thermostat wall plates and cover plates can help if you're also covering gaps or marks around the wall opening.

Is a keyed or combination thermostat lock box better?

A keyed guard suits you if you want a physical key to control access. Most picks here use a key lock, and the Honeywell guards add an inner shelf.

A combination lock may work better when several people need access and you don't want to manage a shared key. Pihode uses a settable numeric code, so decide who should know it and how you'll share it.

Both styles still need a good fit and secure mounting. A lock can't compensate for a cover that is too small or installed on a surface that won't hold it.

Does a thermostat lock box affect temperature sensing?

A cover may change airflow around a thermostat, so look for ventilation and follow the installation instructions. TRJ and Gedreew describe four-sided ventilation, while Pihode describes air vents.

Keep the thermostat away from direct sunlight, drafts and heat sources when possible. Our guide to thermostat placement covers those location checks.

Final choice: which thermostat lock box should you pick?

Choose the Honeywell Home Large Thermostat Guard CG512A1009 if your thermostat needs its wider fit and you want a key lock. Pick the medium Honeywell guard for a smaller compatible control, or Pihode if you want a shareable combination code.

If your thermostat doesn't fit those options, compare the exact interior dimensions of TRJ, Gedreew, JGWPA and GYFVBH before deciding. For help choosing the thermostat itself, start with our guide to thermostats for your home.

Our top 3 picks at a glance

1. 1
   Best for larger thermostats

   Honeywell Home Large Thermostat Guard CG512A1009

   8.4/10 our score

   See it on Amazon
2. 2
   Best for medium-size Honeywell controls

   Honeywell Home Medium Thermostat Guard CG511A1000

   8.2/10 our score

   See it on Amazon
3. 3
   Best for a clear, ventilated cover

   TRJ Thermostat Lock Box with Key

   7.8/10 our score

   See it on Amazon

Frequently asked questions

How do you choose the right thermostat lock box size?

Measure the thermostat's width, height and depth, then compare all 3 numbers with the guard's usable interior dimensions. Leave room for the thermostat's edges and check whether the cover must open toward a battery door.

A guard's outside size is larger than the space available inside.

Will a thermostat guard affect temperature readings?

A cover can change airflow around a thermostat, so look for a design with vents and follow its installation guidance. TRJ and Gedreew describe four-sided ventilation, while Pihode describes an air-vent design.

Keep the thermostat clear of furniture and other obstructions.

Can you install a thermostat lock box without removing the thermostat?

TRJ, Gedreew and GYFVBH describe designs that can be installed without removing the thermostat.

Check the mounting instructions and wall surface first, and allow room to open the cover and reach the thermostat when needed.

Should you choose a key or combination lock?

Choose a key lock if you want a physical key to control access. A combination lock, such as Pihode's, can avoid keeping track of a key and lets you share a code.

Think about who needs access and how you will keep the key or code available.