Consider a chemical factory. Certain rooms may never be empty (control room, security, etc), some have a limit on how many people may be there at any give time, and some contain hazardous materials and no one may stay in there longer than a certain time. Beyond that, in case of evacuation it is necessary to know where everyone is.
I am thinking of wearable badges, probably with WIFi (*) and readers at every door, to scan those entering & exiting.
I could make something cheap and small with a $5 Raspberry Pi Zero and a $2 USB WiFI dongle.. or, maybe BlueTooth, but what about a battery?
Of course, passive RFID wouldn’t require a battery, but could I be certain of reading everyone who passes through a doorway (and what about a very wide door, such as might be found in a factory)?
Really, all that I need is a way to identify people as they pass through doorways flanks by readers. Computing power is not required, but since the Raspberry Pi Zero is so dirt cheap, I might be able to find some other uses (attach a mic & speaker? Any other ideas?).
If I do need a battery, then given an 8 hour working day, plus breaks, plus a margin, then I need 10 or 12 hours battery life.
Does anyone know of an of the shelf solution? Failing that, some thing easy to put together from off the shelf parts?