I have just purchased 4 Kidde fire and carbon monoxide alarms. After installing the batteries and preforming the test, two of the alarms continue to beep at a low decibal every two hours

FULL 'make model (what it is)' in all questions please.

If it is the Carbon Monoxide Detector

https://www.google.com/search?q=Model+46-0315

7 to 10 years, you are overdue.

In accordance with the National Fire Protection Association (NFPA), Kidde recommends replacing smoke and heat alarms every ten years and replacing carbon monoxide and combination alarms every seven to ten years (depending on your model) to benefit from the latest technology upgrades.
28 Mar 2022

When Should I Replace My Carbon Monoxide Alarm? - Kidde

I'm pretty sure that indicates an alarm. The pattern is referred to as "temporal 4" which is the alarm pattern for CO. Either your device is in a bad place or there is an intermittent CO leak which is exceeding the ppm (parts per million) threshold for a given time period. The instructions for the device will tell you what that number is. If you have more than one of these, I would try swapping them to determine if the problen is with the device or the location. Good luck!

Possibly. Does the door close with the battery removed? If so the battery is installed incorrectly.
This is an inexpensive unit, less than $10, and is easily replaced if you can't get the door to close.
If you do decide to replace it, you may want to look into a combination unit which monitors smoke and carbon monoxide if you don't have a carbon monoxide detector already in your home.

replace the battery? hopefully it is not actually reporting carbon monoxide.

usually L6 means low battery.

the battery door may not be closed properly. Or the mounting is not correct and the battery safety switch is still on.

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.

probably time for a new one. Most instructions for these types of units will tell you if it does the chirp after new batteries are installed, the unit has likely become defective. You got your money's worth from the unit. You can get better ones noew likely cheaper than the original one.

YES!!!! If this unit is working properly you should not be in the house. Maximum allowable safety level for an 8 hour period is 50! If you think it's working properly call the fire department! This will cause dizziness,nausea,etc. Let your fire department find the problem! If you don't believe me follow this link to owner's manual but do it quickly: http://www.kiddeus.com/utcfs/ws-384/Assets/KN-COB-B(9CO5)en.pdf