The above plots the indoor temperature and air quality index (AQI) in my living and bed rooms over the past 24 hours. The temperature reading is provided by the BME280 sensor and the AQI from the Plantower PMS5003. The data is recorded using Arduinos and uploaded to an SQL database I host on an old computer in my closet. The plots above remotely access the database and plot the data over time. The sensors and Arduinos cost ~$40. PurpleAir uses the same BME280, PMS5003, and Arduino but charges over $300!