I had to look up flyspeck scale, not heard about it before.

I am not sure what works best to kill them, but prolonged use of detergent isn't that great for succulents (likely for most pants). Soaps that are recommended to use are to be insecticidal soaps, or vegetable-based soaps (like Castile soap and similar). Here is something I found looking up that type of scale (soaps mentioned mean insecticidal soaps):

Biorational insecticides like insecticidal soaps and oils act on scale by desiccation or smothering. They are safer to use but they have no residual toxicity. Mortality is caused by direct contact to the scale's soft body tissue (under the armor). These substances will kill adult scale but, like conventional insecticides, they are also more effective against the crawlers. Soaps and oils will usually require 2-4 applications 3-7 days apart to control an infestation. Soaps and oils can be found wherever conventional chemical pesticides are sold.

Soaps and oils can also cause phytotoxicity, especially to sensitive plants and when the temperatures are very high or very low. Testing on a few plants first is suggested before widespread use.

I had scale in past, and used rubbing alcohol. It may work on flyspec scale too???...Btw, when using, keep plants out of direct sunlight.

I had fly speck scale on broms that I brought from FL. it's very common there.

I haven't discovered it until 6mo later - it's very slow to spread. but very hard to get rid off, since it hides inside the leaves near the stem, where it is hard to reach to remove. I've been treating with indoor systemic (bonide) many times. and thought that I got rid of it. but it came back after awhile.

but it did not spread to other indoor plants, excepts another brom.

Systemic is your only option and you'll need to treat repeatedly. usually it's applied to soil, mixing the time release granules.

I’m apparently the only person on the entire intermet who has had it on anything other than broms for some reason, but I’ve found them on pretty much any kind of succulent. I contacted my local ag college plant diagnostic group to confirm. I will look into bonide. Are there other brands that work as well? I’ve noticed that it’s harder to kill than regular scale, because the female is inside two layers (!!!!) of armor.

One more question— is there any harm to using the outdoor version indoors? my plants are indoors in the winter, outdoors in the summer.

well... It depends on your view on poison :). use proper precautions, read the labels before use. outdoor is stronger and will kill feeding insects, including bees.

some people avoid it for that reason. don't know if your succulents are visited by bees, if not - perhaps it's ok. search for opinions and discussions.

do not put your fingers into soil with systemic, use rubber gloves. skin contact is bad.

also do not inhale/use respirator if in spray form (e.g. Bayer 3-in-1).

systemic is effective over the course of sev months depending on dosage and frequency of watering. it is only effective when the plant absorbed it with water. it takes about a week usually to get into plant tissues. that's why they usually recommend some sort of topical spray application con-current with 1st application.