Safe-T-Alert makes three kinds of 12 V alarm for RVs: carbon monoxide (CO) only, propane (LP gas) only, and combination alarms that detect both. They look similar on the wall, but they watch for two very different hazards. This guide explains the difference, where MTI says each kind belongs, and how to pick the right one.
Two gases, two behaviors
Propane is heavier than air. MTI describes it as sinking and pooling in low areas of the rig, which is why its training material says a propane alarm is mounted near the floor, 4 to 20 inches off the floor.
Carbon monoxide is colorless and odorless, and MTI notes that CO from generators and engines can reach dangerous levels before you notice. MTI's CO training material quotes NFPA 720 (2009): the location for effective performance is not generally dependent on mounting height, because CO's density is similar to air at room temperature and it mixes readily with air. In RVs, MTI says CO alarms and combination CO/propane alarms are installed near the gas appliances, and a second CO alarm can be added in a separate sleeping area for extra protection.
Always follow the location instructions in the manual for your model.
The three kinds compared
| Propane only | CO only | Combination CO + propane | |
|---|---|---|---|
| Safe-T-Alert series | 20, 30, 80 universal | 62 | 25, 35, 45, 85 universal |
| Standard | UL 1484 RV | ANSI/UL 2034 | UL 2034 RV and UL 1484 RV |
| Alarm point | Below 25% of propane's lower explosive limit (20 and 30 Series) | 400 ppm within 4 to 15 minutes | CO and propane points as above, in one case |
| Current draw at 12 V | 75 to 90 mA (20 Series; MTI's web page and price sheet differ), 90 mA (30 Series), 108 mA (80 Series) | 37 mA | 108 mA |
| Extra features | 85 dB horn and self-cleaning sensor (30 Series) | Memory Scan keeps the CO level that set it off | MTI's patented dual-alarm design (25, 35 and 45 Series) |
All of them run on the RV's 12 V supply (no batteries), have an alarm mute button and a rapid-recovery sensor that re-alarms if gas is still present, and are rated from -40°F to +158°F.
Which should you buy?
Your RV has one propane alarm and no CO alarm
This is common in older rigs. MTI's training material says RVIA has required CO alarms in new motorized RVs since October 1993, and in all new RVs only since January 1, 2005. MTI designed its combination alarms to upgrade a single 12 V propane alarm to one that detects both gases, so the simplest fix is a combination alarm in the same spot. Match the size of the old alarm: the 25-741 fits the footprint of a 20 Series, the 35-741 fits a 30-441 and the 35-742 replaces a 30-442. For an odd size, the 85 Series comes with a trim ring.
Your RV has separate propane and CO alarms
Replace each like for like when it reaches 5 years, or combine them into one combination alarm near the gas appliances and keep a CO alarm in the bedroom. The 62 Series draws just 37 mA, which is easy on a house battery.
You want the alarm to shut off the gas
The 25-742-R kit pairs a flush-mount combination alarm and trim ring with a solenoid valve so the alarm can control the LP supply. If your current valve is controlled by a CCI propane alarm, MTI warns never to connect a Safe-T-Alert alarm to it; MTI says the CCI alarm and valve must be replaced together by its 35-742-R-KIT. Send us a photo and we will advise.
You have a marine or home application
Buy the model listed for that use. MTI says never to install a residential CO alarm in an RV, and the alarms on this page are the RV models.
Frequently asked questions
Does a CO alarm detect propane?
No. The 62 Series detects carbon monoxide only. For both, choose a combination alarm.
Where does a combination alarm go if propane sinks and CO mixes with air?
MTI says CO and combination alarms in RVs are installed near the gas appliances. Follow the mounting instructions in your model's manual.
Do the alarms drain my battery?
They draw a small, constant current: 37 mA for the 62 Series CO alarm and 108 mA for the combination alarms, per MTI. If you use a battery disconnect in storage, remember it also switches the alarm off, so only do that when nobody is using the RV.
Are combination alarms less sensitive?
MTI lists the combination models as conforming to UL 2034 RV and UL 1484 RV, the CO and propane standards for RV alarms.
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.