With a PIR sensor one can detect movements within it’s field of view and trigger other hardware, such as surveillance cameras. It is also possible to record the frequency of movements over time, e.g. to monitor motion activity in a room of your apartment.
With a PIR sensor attached to my RasPi, I recorded motion events by storing UNIX timestamps in a single-column MySQL table. I wanted to visuaize these data points as a histogram displaying the frequency of motion events over time, but this task turned out to be more complicated than expected using GNUPlot. So here’s a short tutorial how it works: