A fire alarm can warn you about smoke. A carbon monoxide alarm can warn you about CO. But what if one device could provide both types of protection?
That is the basic idea behind a 2-in-1 smoke and carbon monoxide alarm.
For homeowners, renters, landlords, and families, combination smoke and CO alarms can simplify home safety by bringing two important detection functions into one residential alarm. However, choosing the right device is about more than simply looking for the words "smoke" and "CO" on the package.
You also need to understand what the alarm detects, where it should be installed, how it signals different hazards, how often it should be tested, and what you should do when it sounds.
The Heiman HM-636THS is designed as a residential combination Smoke/CO Alarm, with separate smoke and carbon monoxide alarm functions in one device. Its specifications include a 10-year non-replaceable lithium battery and an alarm sound level of at least 85 dB at 10 feet. The product is identified with UL 217 for smoke alarms and UL 2034 for carbon monoxide alarms.
Let's look at what that means for an ordinary American home.
What Is a 2-in-1 Smoke and CO Alarm?
A combination Smoke/CO alarm combines two different detection functions into a single residential device.
The distinction is important.
The smoke portion is designed to respond to smoke that reaches the smoke sensor. It is not intended to detect gas, heat, or flames.
The CO portion is designed to respond to carbon monoxide at the CO sensor. It is not a general-purpose gas detector and should not be treated as a combustible-gas detector.
In other words, a combination alarm does not mean that one sensor detects everything.
Instead, two different hazard-detection functions operate within the same alarm housing.
That makes the device particularly useful for residential environments where homeowners want both fire and carbon monoxide protection without installing two separate alarm housings in every location.
Why Carbon Monoxide Protection Matters
Carbon monoxide is particularly dangerous because people cannot rely on their senses to detect it.
CO is colorless, odorless, and poisonous. It can be produced by fuel-burning equipment involving wood, coal, charcoal, oil, natural gas, gasoline, kerosene, or propane.
Potential sources in a home include portable heaters, gas or wood-burning fireplaces, gas ranges or cooktops, and gas clothes dryers.
Problems can also occur when venting is damaged, blocked, disconnected, or otherwise inadequate.
This is why a CO alarm is different from simply having a smoke alarm.
You may smell smoke.
You cannot smell CO.
A home can therefore have a serious carbon monoxide problem without producing an obvious warning that people can detect themselves.
What Does the HM-636THS Detect?
The HM-636THS provides two distinct forms of protection:
· Smoke detection
· Carbon monoxide detection
The two functions have different alarm patterns.
For a smoke alarm condition, the alarm uses a red LED and a distinctive audible sequence. For a CO alarm condition, the red LED flashes four times every five seconds, accompanied by four beeps every five seconds during the initial alarm period.
This distinction can help occupants recognize what type of hazard has triggered the alarm.
The device also maintains an alarm-memory indication if an alarm occurred while the user was away. In that situation, the red LED flashes once every 20 seconds as a reminder. The indication can be cancelled by pressing the Test/Hush button or will stop automatically after 12 hours.
For a homeowner, this is useful because an alarm may have detected an event while nobody was home.
Why One Device Can Be More Convenient
The obvious benefit of a combination alarm is simplicity.
Instead of installing one smoke alarm and one CO alarm in the same area, a combination device can provide both functions in one housing.
That can be useful in:
· Bedrooms
· Hallways
· Living areas
· Multi-level homes
· Homes with fuel-burning appliances
· Apartments and townhouses
· Guest rooms
However, convenience should never be confused with "one alarm is enough."
The device only detects smoke or CO that reaches its sensors.
A smoke or CO problem on another floor may not be detected quickly by an alarm installed elsewhere. The product information therefore recommends coverage on every level, in every sleeping area, and in every bedroom.
Where Should You Install a Combination Alarm?
For a typical home, recommended locations include:
· Every level of the home
· Every bedroom
· Inside bedrooms, particularly where doors may be closed during sleep
· Hallways near sleeping areas
· Near the top of stairs
· At the bottom of basement stairs
For additional protection, alarms can also be installed in other rooms and storage areas where temperature conditions are appropriate.
Ceiling installation should generally place the alarm as close to the center of the ceiling as possible.
If wall mounting is allowed by local building codes, the top edge of the alarm should be positioned between 4 and 12 inches from the wall/ceiling line.
In either case, the alarm should be at least 4 inches from where the wall and ceiling meet.
Where Should You Avoid Installing It?
Location can affect how quickly smoke or CO reaches the sensor.
Avoid placing the alarm:
· In garages
· In furnace rooms
· In crawl spaces
· In unfinished attics
· In extremely dusty or greasy locations
· Directly next to cooking appliances
· In extremely humid locations
· Near ceiling fans or open windows where turbulent air may interfere
· In direct sunlight
· In areas below 40°F or above 100°F
· Near fluorescent lights
· In dead-air spaces
The device should also be kept away from combustion sources when possible.
The product guidance recommends at least 20 feet from sources such as stoves, furnaces, water heaters, and space heaters when possible, while recognizing that smaller homes may not allow this distance.
A 10-Year Battery Does Not Mean "Install It and Forget It"
The HM-636THS uses a 3V CR-2/3AZ lithium battery with a stated 10-year battery life, and the battery is not replaceable.
A long-life sealed battery can reduce the inconvenience of frequent battery replacement.
But homeowners still need to:
1. Test the alarm weekly.
2. Keep the alarm clean.
3. Pay attention to warning signals.
4. Replace the alarm when it reaches end of life.
5. Replace the alarm immediately if it fails testing.
The product guidance specifically calls for weekly testing.
What Does the Test/Hush Button Do?
The Test/Hush button has multiple purposes.
Pressing it for approximately one second can initiate the alarm test.
The test sequence includes audible and visual indications designed to verify that the alarm is functioning.
The Hush function can also temporarily silence certain unwanted alarm conditions.
For smoke, the alarm can remain silent for up to 10 minutes. If smoke remains or continues increasing, the alarm returns to alarm mode.
For CO, the hush period is up to four minutes. If the CO level remains potentially dangerous, the alarm will sound again.
This is an important distinction:
Hush is not the same thing as turning off the alarm.
It is intended to give the homeowner time to identify and correct a situation.
It does not eliminate smoke or CO.
What Happens When the Battery Is Low?
A low-battery condition produces a warning pattern.
The product information specifies LED indications and periodic audible chirps associated with low battery and other warning conditions.
The Hush feature can temporarily silence the low-battery warning for up to 12 hours.
But silencing a warning does not solve the underlying problem.
The battery condition still needs attention.
What Happens at End of Life?
A smoke/CO alarm is not designed to operate indefinitely.
When the alarm reaches its end-of-life warning stage, the unit should be replaced immediately.
The product documentation specifically states that an alarm giving an end-of-life warning should be replaced and that the device will no longer provide detection once its service life has ended.
This is one reason homeowners should not simply remove a troublesome alarm because it is old.
The correct response is replacement.
What Should You Do If the Alarm Sounds?
Never assume an alarm is a false alarm simply because you do not immediately see smoke or feel sick.
If the smoke alarm sounds, get everyone out of the home and follow your family's fire escape plan.
If the CO alarm sounds, move everyone to fresh air immediately, check that everyone is accounted for, and do not re-enter until emergency responders have arrived, the premises have been aired out, and the alarm returns to normal. The guidance also recommends contacting the local emergency service or 911.
Final Takeaway
A 2-in-1 smoke and carbon monoxide alarm is more than a convenient combination of two products.
It provides two different types of residential hazard detection in one device.
For homeowners, the most important principles are simple:
Install enough alarms. Place them correctly. Test them every week. Keep them clean. Never ignore an alarm. Replace them when required.
The HM-636THS is designed around that approach, combining smoke and CO detection, a 10-year non-replaceable lithium battery, audible and visual alarm indications, Test/Hush functionality, and residential placement guidance.
A combination alarm cannot replace an overall fire-safety plan—but it can become an important part of one.