Friday, September 4, 2020

Inside Digital Pregnancy Tests

Tom Warren (Hacker News):

Pregnancy tests used to be fairly simple sticks you peed on, but the move to digital versions has transformed them into tiny computers almost as powerful as the original IBM PC. Fascinated by the digital era of pregnancy tests, Twitter users foone and xtoff recently pulled apart examples from Walmart and Clearblue to reveal what’s really going on inside.

Each test, which costs less than $5, includes a processor, RAM, a button cell battery, and a tiny LCD screen to display the result.


You might assume that the addition of an LCD screen and processor to digitize this pregnancy test improves the accuracy or modernizes how the test works, but that’s certainly not the case. This digital pregnancy test still includes a paper strip to measure the chemical reaction you create when urinating on the strip.

It’s an interesting user interface problem. Even if the paper strip is the same, the digital tester is probably more accurate because it has been calibrated based on actual strips, whereas the human is reading instructions on the box and may not have seen a variety of actual positive and negative results. The digital test is also less stressful because it gives a definitive result without having to wonder whether one read it properly. How faint a line is too faint to count? Is it just an evaporation line?

The downsides are that the single-use digital test is more wasteful and that the binary result is not 100% definitive. It can in rare situations report a false negative instead of a faint positive. With the analog test, the faint positive would be a sign that you should test again later or that hormone levels were off for some other reason that might warrant investigation.

Update (2020-09-07): foone:

Yesterday I had a lot of retweets and reddit posts and such for playing Doom on a pregnancy test. But as I explained then, it wasn’t really PLAYING on a pregnancy test, it was just a video being played back, not an interactive game.

Well, now it is. It’s Pregnancy Test Doom!

2 Comments RSS · Twitter

It is pretty awful for the environment... at least they could have made the electronics reusable, so you could put a new strip into the same tool.

>The paper strip inside acts like a wick so when it
>gets wet it activates the battery and powers the
>device on

Using the strip both for the actual test, and to turn the device on, is such a clever idea.

But putting computers into single-use throwaway devices that could basically just be a strip of paper, and work essentially the same, is kind of bonkers.

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