Alarm went off but no smoke was found and no other smells were detected. I do not believe that there was CO present. All the units were activated. after a period of time they stopped. This occurred 3 times within about 1.5 hours. On one unit a red light blinked. Not sure if another unit blinked

a smoke alarm yes

Most smoke alarms depend on a mirror and laser. If the one is question is near a bathroom, it probably went off after someone took a shower? The steam from the bathroom will fog the mirror and set it off. Same problem if it is near a source of cold air on a cold day with heat on in the house. If the problem is cold air from the attic, go to the attic and move the insulation. Seal the hole for the wires with canned foam like Great Stuff, and put the insulation back over it.

It sounds like you have a CO detector, or a combo smoke/CO detector. The alarm you are describing indicates that the unit is sensing carbon monoxide. If you are sure that none is present and the detector is mounted in a location suggested by the documentation, the detector is bad and should be replaced.

The unit probably needs replacing (every 10 years by code for 120V smoke alarms; NFPA 72). Note that most 120V devices are of the ionization type and must be disposed of appropriately. The label on the under side of the device often has instructions. Also try searching for your model on the manufacturer's website.

The constant green LED means the alarm has AC power.
A flashing green light every 2 seconds without an audible alert means the unit recently sounded ( was the one activated ) and is now in latching mode to let you know that it was the unit that detected the problem. To clear the latching mode hold down the test button for 5 seconds.
Red LED flashing once per minute means that the back-up battery is connected and functioning.
Red light flashing constantly during alarm means that it is the unit that initiated the alarm siren.

send the detector back and have it replaced,
The CO sensor will not alarm to levels of CO below 30 ppm and will alarm in the following time range when exposed to the corresponding levels of CO: 70 ppm CO Concentration 60 - 240 minutes 150 ppm CO Concentration 10 - 50 minutes 400 ppm CO Concentration 4 - 15 minutes The alarm shall include a piezoelectric horn that is rated at 85 decibels at 10 feet. When the unit detects carbon monoxide, the alarm pattern will be four (4) short beeps - followed by five (5) seconds of silence - followed by four (4) short beeps. The unit shall incorporate 2 LED's. A green LED will be illuminated to indicate the alarm is operating properly when plugged into an outlet, and will flash every 10 seconds when on backup battery power. A red LED will flash to indicate that carbon monoxide has been detected until the device is reset or CO is eliminated or will flash to indicate low battery or alarm malfunction. The unit shall at a minimum meet the requirements of CAN/CSA 6.19-01. It shall also include a 10-year manufacturer's limited warranty or

Test/Reset Button - Tests the unit for proper operation. Resets the carbon monoxide alarm.
• Tamper Resist Feature - If activated, unit goes into constant alarm mode if it has been unplugged or has come loose from the outlet.

Besides the obvious jokes about gas in the bathroom, I would advise you move it out of the bath room. It is being affected by excessive moisture causing errors in the sensors. The same can happen for smoke alarms with condensation or other moisture sources. It should be located relatively close to a possible source of problem, but not right on top of it.

Is the shower in use at around 7 am every AM?

Normally this means the smoke detector's battery or batteries are getting weak and need to be replaced. Since your detector incorporates carbon monoxide detection it could also mean the sensor that measures CO is going bad. Most units with CO detection have a life expectancy of 8-10 years. If your unit is that old I would suggest replacing it. Hope this helps.

All smoke detectors, whether they are of the photo-electronic or ionization type, can false alarm due to steam. There are basically two solutions to your problem. Either move the detector further away from these areas (I have found keeping a smoke detector at least 6 feet away from the bathroom door normally works) or if that is not practical, after showering try to evacuate steam by either opening a window or turning on the exhaust fan for several minutes before opening the bathroom door.

sounds like a smoke detector to me. usually they just break the red or the green through a relay, if it smells smoke. could be dust burning off the heat strips first use, or you could get on the roof and find burned wires or motor. lots of old wires burning up with heat strips kicking in this time of year. i usually have em turn off alarm so fire dept wont come and turn to max heat and burn off the strips , measure amps, check wires, and all relays etc. you may have to bypass smoke detector till done. then return to correct "as found" wiring and reset alarms. hopefully no call backs. good luck.