It is easy to mock the OTT solution that has gone on here, however...

I had the pleasure of working with a deaf guy that would spend an inordinate amount of time in the loo. There was just the one loo.

45 minutes could pass by with him occupying the loo. Being deaf it wasn't as if you could knock on the door and ask him to hurry up - he would not be able to hear you, and, even if he could hear you he would be able to pretend otherwise. Like Schrodinger's cat there would be no way of knowing...

You couldn't complain either, for all one knew he might have been using that time for something more important than one's own toiletry needs. Perhaps it was the batteries in his hearing aids, not being deaf one would not know, or even know if speculating about such a thing was morally inconsistent. Or maybe he had another medical condition that one was not privy too. Or maybe his body jewellery needed to have puss and inflammation cleaned out if it on a regular basis. One can only imagine...

It wasn't as if he took the newspaper in or his phone, so it wasn't a really good book or jolly exciting porn collection that took up his time there. None of the micro-managers really thought it a problem that he would spend such a long time in the loo, even if other staff and visitors had to go to a nearby Starbucks due to being caught short.

So we had a 'is the toilet free' messaging system of our own. There would always be euphemisms, it wasn't as if we would message 'finally [x] has finished having a poo and you can now use the loo'. Anyone shoulder surfing our screens would not realise that that messaging conversation in the corner about 'that report being delivered', 'the printer having finished', 'those files uploaded' or 'desperate for that CSV file' was about the status of the loo. However, through such messages, those two floors away from the loo would be able to find out if it really would be possible for them to relieve themselves or not.

In our case, of a small team with inadequate toilet facilities, we really should have moved to a proper modern office with all of those Philips controls in the toilets to know what the occupancy situation is, whether the loo needs to be flushed, whether the water in the hand basin needed to flow and so on. But we were not going to do that. So we had our own system, a system that manager types were not privy to. It worked well for us and it was fun.

Had we gone a bit further, hooked up that free Raspberry Pi nobody knew what to do anything with and implemented something similar, I don't know how it would have panned out. Someone other than the loo-hogger would have been sacked for wasting company time and not prioritising their work, the politics of disability would have got ugly and it would not have happened. So, even though the solution of the Raspberry Pi is OTT, in getting it done and having fun doing it, I think that this team have got something out of it a lot more valuable than their 'Heath Robinson' toilet status indicator.

Personally I like the simple solution they have on older trains - a light that shows 'vacant' or 'occupied'. There is no internet to break down, there is no TCPIP settings to get wrong, just a lightbulb to change and a switch to keep clean. I am sure that for multiple stalls the series/parallel could be worked out for the switches without too much difficulty.