1. Smoke alarms are easy. Press the test button, if it alarms, the circuits are working. The internet (eHow.com) says not to light something on fire to test them because you’ll wear them out and won’t work when u have a real fire, even if the test button still works (it only tests the circuit, not the smoke detecting).

2. Carbon Monoxide, CO2 detectors are easy too, same test button tests the circuit, but you should also have at least one with a number readout. Mine reads 0 PPM (parts of CO2 per million) and alarms at 400 PPM. This you want to test with something that takes up oxygen. I used a smoking incense held 8 inches below and in 30 seconds the reading went up to 41 PPM then 100 PPM. (doityourself.com)

The detectors will also have a date on them and possibly a replace by date. Mine all say replace in 10 years with new ones. If you hear chirping you should replace the batteries. Daylight Savings Time is a good time to check detectors since it is twice a year.