The quickest way to pick a replacement Safe-T-Alert alarm is by size. A new alarm that is smaller than the old one leaves a hole or a paint line on the wall; one that is bigger may not fit the space. This guide lists the case size MTI publishes for every Safe-T-Alert RV alarm we stock, plus the cutout and trim-ring sizes where MTI gives them. All sizes are width x height x depth, in inches.
How to measure your old alarm
- Switch off the 12 V supply to the alarm (battery disconnect or fuse).
- Measure the face of the old alarm: width, height and how far it sticks out from the wall.
- Remove the screws and pull it out. If it sat in a hole (flush mount), measure the hole. If it sat on the wall (surface mount), note the screw positions.
- Write down the model number and date code from the label, then compare with the table below or with our Safe-T-Alert replacement chart.
Safe-T-Alert sizes
| Series | Detects | Mount | Case size (in) | Cutout / trim ring (in) |
|---|---|---|---|---|
| 20-441-P | Propane | Surface | 3.5 x 2.5 x 1.25, plus 0.25 bracket | n/a |
| 25-741 Mini | CO + propane | Surface | 3.5 x 2.5 x 1.25, plus 0.25 bracket | n/a |
| 25-742 Mini | CO + propane | Flush | 4.5 x 3.25 x 1.25 | Cutout 3.25 x 2.5 |
| 25-742 with trim ring | CO + propane | Flush | 7 x 4 x 1.25 with trim ring | Cutout 3.25 x 2.5 |
| 30-441-P | Propane | Surface | 6 x 1.875 x 1.25 | n/a |
| 30-442-P | Propane | Flush | 6.375 x 2.875 x 1.25 | not published |
| 35-741 | CO + propane | Surface | 6 x 1.875 x 1.25 | n/a |
| 35-742 | CO + propane | Flush | 6.375 x 2.875 x 1.25 | not published |
| 45-741 | CO + propane | Surface | 4.25 x 2.5 x 1.25 | n/a |
| 45-742 | CO + propane | Flush | 4.75 x 4.75 x 1.25 | not published |
| 62-541 | CO | Surface | 3.5 x 2.5 x 1.25, plus 0.25 bracket | n/a |
| 62-542 with trim ring | CO | Flush | 7 x 4 x 1.25 with trim ring | not published |
| 80-441 universal | Propane | Surface, trim ring | 4.25 x 2.75 x 0.75 | 7 x 4 x 1 with trim ring |
| 85-741 universal | CO + propane | Surface, trim ring | 7 x 4 x 1 with trim ring | trim ring included |
What the sizes tell you
Three footprints repeat across the range
The small 3.5 x 2.5 in surface case is shared by the 20 Series propane alarm, the 25-741 Mini CO + propane alarm and the 62-541 CO alarm. MTI says the 25-741 is the same size, shape and mounting as the 20-441-P, so it drops into the spot of an old 20 Series and adds CO protection.
The long, narrow 6 x 1.875 in surface case is shared by the 30-441-P and the 35-741. MTI says the 35-741 has the same size, shape and mounting as the 30-441-P, which it notes has been installed by RV makers since 2001.
The 6.375 x 2.875 in flush case is shared by the 30-442-P and the 35-742, and MTI says the 35-742 replaces all 30-442 propane alarms without modification.
Trim rings hide an old, larger hole
The models with "TR" in the part number come with a trim ring that covers existing screw holes and lets a newer unit fit into a previous installation cutout. With the ring fitted, the 80 and 85 Series measure 7 x 4 x 1 in and the 25-742-TR and 62-542-TR measure 7 x 4 x 1.25 in. If the old hole or paint line is bigger than a standard model would cover, a trim-ring model is usually the tidy choice: the ring measures 7 x 4 in overall, so the old hole has to be comfortably smaller than that. MTI does not publish a maximum hole size, so measure first or send us a photo.
The 80 and 85 Series are thin
The 80 Series case is 0.75 in deep, and both universal models measure 1 in deep with the trim ring fitted, so they stand out from the wall less than the 1.25 in deep cases. That helps in a narrow aisle.
Frequently asked questions
Which Safe-T-Alert has the smallest face?
The 3.5 x 2.5 x 1.25 in case used by the 20-441-P, 25-741 and 62-541 surface-mount alarms.
What size hole does the 25-742 need?
MTI lists a 3.25 x 2.5 in cutout for the 25-742 and the 25-742 with trim ring.
My old alarm left a bigger hole. What now?
Choose a trim-ring model (80, 85, 25-742-TR or 62-542-TR). The ring covers old screw holes and fits into a previous cutout.
Do all sizes run on the same power?
Yes. Every alarm here is 12 V DC hard-wired, with an operating range of 12 V plus or minus 15%.
Every Safe-T-Alert alarm we sell ships from our warehouse in Upland, California. Not sure which one replaces yours? Send us a photo of the old alarm and its label before you order and we will match it. Browse the full Safe-T-Alert range.