A hall effect sensor mounted to the door frame tells me what angle the door is opened to. When I plotted output over angle, my data wasn’t exactly linear but good enough for an electric door opener.

The NEXIS system supports standard measurement profiles such as Linear, Circular, ... Sensor Concepts has a deep legacy of providing field-level measurement systems for 5th and 6th generation ...

The AH4930Q operates on supply voltages from 2.8V to 5.5V, and a temperature range from -40°C to +125°C. The 3D linear Hall effect sensor is housed in the industry-standard 6-pin SOT26 (Type A1) ...

The linear sensor consists of a linear InGaAs photodiode array, which is connected to 2 integrated p-on-n readout circuits. The pixel operability is > 99% and the quantum efficiency is > 70% at 1550 ...