Sure, but that doesn't tell you if the gearing has bound up or the motor is trying to turn something and it's jittering back and forth (or a small trail of smoke has emitted from the motor 3 hours ago). Plus it's a fun thought exercise.

This came to mind because I recently had reason to set up automated sump pump monitoring for a rental property which doesn't have a proper basement, just a crawl space.

We had the choice of just installing a binary state (wet or not wet) zigbee liquid sensor, which we did, talking to a cheap USB dongle and home assistant, just above the height of the sump pump. But in addition to that I put a $60 camera which has a medium-wide overview of the whole crawl space, generally centered on the sump pit so that it can be checked in the event the liquid alarm goes off.

Stapled some cat5e across the floor joists that comes up through a small hole in the utility room where the PoE switch is. Theoretically it should also serve to check for things like "are raccoons inhabiting the crawl space?" or a few other possibilities.

Heard similar stories from many people. I have my own--

I was at a range shooting this old revolver with worn seals. Every shot, unburnt (or sometimes burning) powder was flying backward onto my face and arms. I basically took a gunpowder shower.

Got up like 6 hours later and went to the airport to get on a plane. Got swabbed. Came back negative. Got on the plane.

So... yeah, not really sure what the swabs are doing. I have to assume it's more an issue of "they're not intending to detect that" than "failures to detect" because otherwise the repeated misses here are just a little too big to believe.

Ion mobility spectrometry is the tech that powers these, and they're VERY sensitive and VERY prone to false positives because it's just looking for ion signatures ("I smell a nitrate/glycerin/etc."). I'm not sure if they're changing modes on the machines between swabs or something, but the machine is a cue for more in-depth inspection, not "zomg I found a bomb". So, some repeated scanning to rule out a false positive or burn off gunk that's accumulated in the machine i.e. we just got a speck of something on the wand or something is gunking up the scanner as opposed to "someone covered in residue that is scary".

Or to assume it's a false positive.

Shortly after 9/11 I was flying out of Hawaii back to the mainland and I watched the screen when they swabbed my bag. It reported as positive for every single type of explosive (to the best of my knowledge, I was not carrying anything even remotely explosive). The tech looked at the results, said "that can't possibly be right" and waved me on.

In my experience if they test positive the tech will stop and wipe down the machine before trying again. They're highly prone to false positives.

Apparently! That or I just have a trustworthy face haha

If this was in the US, it's all security theater. Basically if you get flagged, they swab everything in your bag to find what's getting flagged, and if it's legitimate they pass you through, or they keep swabbing you if its just your hands/arms because they also inspect your bag. It's kind of dumb, but also kind of makes sense.

For extra fun times, baby wipes / wet wipes get flagged as explosives in the US when they use the sniffer devices.

In my experience, UK airports seem to not want you to leave the country — contra to the perception the government project regarding not wanting you to stay in the first place. :/

Had a number of experiences where their identity scanners (for some destinations they scan you at the start of security and just before the gate to ensure you get on the right aircraft) failed to be operational resulting in delays that ultimately may have forced me to miss my flight and stay in the UK. On the other hand, arriving from Ireland to the UK results in no checks because of the common travel area — you get waved through a special gate which is reserved for passengers from Ireland. LOL

Fred is a great YouTube rabbit hole... His "Age of Steam" series for the BBC is fantastic.

https://www.youtube.com/watch?v=kl_UA36ouzM&list=PL2vJ5Cg-wl...