Have you considered taping a sensor to the light, or measuring the electrical current flowing through the power cord? Both should be a bit more reliable. The idea of messing with mains power is scary at first but with basic precautions it's fine, and I think you can buy current meters with various interfaces if you aren't comfortable.
Why would I buy power meters and mess around with indirect signals that don't measure what I want (how much time is left on the cycle) and instead just tell me whether it's running?
I already have an old webcam and raspi I'm not using, and they measure exactly what I care about.
> how much time is left on the cycle
Ooh, new requirement!
Set timer on phone when setting timer on machine...
Ah, but my washer and dryer love to lie to me and add 20 minutes to the cycle because they're "eco-friendly". And this is mostly to help my wife who has a brain injury and can't remember to set a timer.
> this is mostly to help my wife who has a brain injury
Sorry to hear that. Hope things get better. Don't know if your wife's case fits, but the brain has a lot of plasticity; fingers-crossed.
> my washer and dryer love to lie to me and add 20 minutes to the cycle
We're going to have to assign a business analyst here to capture the full slate of requirements before we start development, i.e., armchair suggestions :-) I don't think agile is working very well here
You see, you're trying to paint the bike shed after I've already built a pole barn for my ATVs.