You can get the ones with indicators, which change color according to how saturated they are.

You can check the color to see whether it's time to microwave them, and whether they are dry once you microwaved them.

The indicator is supposed to be toxic though. I’ve always seen warnings to never reuse that kind.

If the indicator is cobalt chloride, which is blue when dry and pale pink (possibly almost invisible) when wet, that can be toxic or carcinogenic when ingested in great quantities, or when you inspire a lot of dust of it, but it is not dangerous to handle when in compact form.

It is certainly not something like a poison, where small quantities can have harmful effects, at least not for most people.

Like nickel, cobalt can cause allergies in some people, in which case repeated exposure can have serious effects even in small quantities, in those humans who are sensitive to it.

I use them in my car against condensation.

The instructions on tge cover say 3 minutes at 700W in the microwave.