A few days ago, Tiff sent me details of a beekeeping electronics project, Easy Bee Counter (also on Instructables). Sometimes we wonder if bees are coming and going, as a rough indicator of hive health, queen health or just for reassurance about the quantity of stores, and this project aims to answer that question.
Once fitted to the hive, the bees are forced to go through one of twenty-four gates where LED/photodiode pairs detect presence and direction of movement. The counter is based on Adafruit Arduino microcontrollers (Feather and ItsyBitsy), and a PCB which can be ordered for around $20.
The resulting plots can tell you more about your colonies without disturbing them, including the rate of increase or decrease of foraging or orientation flights, or distance to a pollen or nectar source.