As @Kwpolska says, mostly they have reverse engineered Bluetooth protocols. I'm on my work computer (that's fiercely monitored) so can't give you much links rig

As @Kwpolska says, mostly they have reverse engineered Bluetooth protocols. I'm on my work computer (that's fiercely monitored) so can't give you much links right now, but Buttplug site has information about all the messages and protocols. And some of them are quite a mess. Some of them, like Lovense, have said they had intention to publish APIs, but they just have some empty repositories in Github. (Lovense is a weird company, everything points to just one or two persons in [IIRC] Taiwan. They're very opaque.) And some have been fishy too. There have been class actions against brands like Hytto / Lush [0] or We-Vibe [1] -- 0: https://www.courthousenews.com/judge-forwards-class-action-suit-against-adult-toy-maker/ https://www.courthousenews.com/judge-forwards-class-action-s... 1: https://topclassactions.com/lawsuit-settlements/lawsuit-news/vibrator-maker-pay-3-75m-settle-privacy-class-action/ https://topclassactions.com/lawsuit-settlements/lawsuit-news...