I already have a PM2.5 AQI Sensor at hand. It is very good with showing the air pollution indoors, esp. if someone smokes around i can definitely see it as the value goes up to 600. Otherwise it is between 20-40 which shows that it is OK.
However what i am trying to achieve is that my son sits in the his room playing video games or working on the computer, with his door shut (1st requirement of puberty for a teenager!

As i only have PM2,5 sensor at hand i roughly know now what it shows. But i still don't have any idea on CO2 and PM10. As i know a CO sensor looks for lpg or any other hazardous gases. Does anyone of you have any simple layman's terms on what each and every sensor type shows, as i do not have any scientific degree on pollution!
Also; what type of sensor to use in my son's room, to remind him of opening the door or window for some fresh air, besides opening his room door and yell him to leave the room door open

Thanks...