It's not an "if" detector, it's a "how much" detector. It looks like it's using the LED chamber to light the film in a consistent way, and then the phone camera measures the color change to quantify how much radiation it was exposed to.
There's always the Jewel Cooler:

I mean, it is 100% discrimination against people who are too old to do the job, yes.
15 square meters isn't the same as 15m×15m, it'd be a little smaller than 4m×4m. Still a big hole.
More like homicidally stupid.
The 'S' in IOT stands for Secure
We definitely whip shitties in WI, too.
For those wondering, this played out well! OP found someone to take the job. His wife bit on the prank gleefully, was actually thrilled by the idea that OP had a son he didn't know about. When the prank was revealed, she thought it was hilarious. Ultimately pretty wholesome, OP married a keeper.
Generally, when describing a thing, the unit is written as singular. "15 minute delay", "10 foot pole", "5 gallon bucket". When referring the unit itself though, it would be plural: "a delay of 15 minutes", "the pole is 10 feet long", "this bucket holds 5 gallons". I'm sure there's a more precise way to say this, but hopefully it helps.
The vegetable vampire one was Bunnicula!