Environmental sensors provide a fairly simple ways to collect a variety of different data about the environment, for example air quality measurements using particle counters, CO, CO2 or O2 sensors and more basic humidity and temperature. Sensors are – depending on model – available as analogue or digital sensors with different protocols. 

====== Temperature / Humidity ======
The list below presents a small collection of common, cheap digital sensors

===== Sensors and specifications =====
^AM2302^AM2320/AM23212^SHT71^HTU21D^SI7021^BME280^
|Operating range|0-100|0-100|0-100|0-100|0-100|0-100|
|Absolute accuracy|
|(%RH @ 25°C)|±3% (10-90%)|
|±5% (<10%, >90%)|±3% (10-90%)|
|±5% (<10%, >90%)|±3% (20-80%)|
|±5% (<20%, >80%)|±3% (20-80%)|
|±5% (<20%, >80%)|±3% (0-80%)|
|±5% (>80%)|±3% (20-80%)|
|Repeatability|±0,3%|±0,1%|±0,1%|-|±0,025%|-|
|Long term stability|0,5% p.a.|0,5% p.a.|0,5% p.a.|0,5% p.a.|0,25% p.a.|0,5% p.a.|
|1/e Response|5s|5s|8s|5s|18s (with cover)|
|17s (without)|1s|
|Supply voltage|3,3 - 5V|3,3 - 5V (AM2320)|
|2,6 - 5V (AM2321)|2,4 - 5V|1,5 - 3,3V|1,9 - 3,3V|1,7 - 3,3V |