UEi Test Instruments AQM4  Air Quality Meter, 1-Pack Max and min functions included (TWA and STEL for CO2 only) 99 points manual recording 8000 points auto recording Large LCD display designed with NDIR waveguide technology CO2 sensor programmable CO level alarm extended drift compensation on CO2 sensor Audible alarm (~80db) threshold setting Usb cable and software included Ac power adaptor included and 4 aa batteries