DHT11 Sensor

The most common starter sensor for environmental monitoring, giving both temperature and relative humidity over a single data wire. Cheap, reliable and well supported by libraries. Its limitations are honest ones: it reads in whole degrees and whole percent, is accurate to about plus or minus 2 degrees, and must not be polled faster than once per second. For weather stations and room monitors it is perfectly adequate; for anything needing precision, step up to the DHT22. Temperature and humidity from one sensor and one pin; Very well supported by Arduino libraries; Calibrated digital output, no analogue conversion needed; Low cost for classroom and hobby use