PT&Key PTtech Carbon Monoxide Checker

Purchased on Amazon in 2022.
Although not shown in the photos, the instruction manual is included. Operation has been confirmed.
Below is the product description from Amazon.

[Includes Batteries and Storage Pouch] This device uses an electrochemical sensor system powered by 2 AAA batteries. It is a compact and stylish model with approximately 2 years of continuous operation. 1. Remove the back cover and insert the batteries. A short beep will sound. The sensor will enter detection mode in about 30 seconds. The detection range is 25 square meters. When no gas is detected, the green LED lamp will flash every 30-40 seconds, and the device will enter standby mode. 2. Test Button. Pressing the test button will illuminate the alarm lamp and LCD display, and the alarm will sound 4 times, with a 2-second pause between sets of two beeps. The volume is 80dB. The display will enter power-saving mode and turn off after a while. The included mesh bag does not interfere with the sensing function, but please use it so as not to block the vents on the front and back.
[Alerts with Light and Sound] Alerts you to danger with a three-stage system: a flashing red alarm lamp, a loud alarm sound, and an LCD display showing the concentration level. [No Display] Normal. The green LED lamp flashes every 30-40 seconds. [30ppm-] Alarm sound and red lamp flashing if it continues for over 2 hours. [50ppm-] Alarm sound and red lamp flashing within 30-90 minutes. [100ppm] Alarm sound and red lamp flashing within 10-40 minutes. [300ppm-] Alarm sound and red lamp flashing within 3 minutes. [500ppm-] Immediate alarm sound and red lamp flashing. *This device sounds an alarm when the concentration exceeds a certain level and is not a real-time monitor or measurement device.
[World Standard Product] Features a reliable and cost-effective electrochemical sensor with a proven track record. It is a world-standard product with proven quality, selling millions of units annually worldwide, including China, Europe, North America, the Middle East, and Southeast Asia. Furthermore, it undergoes inspection in Japan to ensure product quality. Operating temperature: -10-40℃, Operating humidity: 20-90%. Sensor lifespan is approximately 5 years.