From what I understand from what has been said, he is receiving treament, as a result of what he has done. It certainly does seem to me that what he did has definitely triggered appropriate alarms and made sure he is getting help.
When this sort of thing happens, a judgement call has to be made as to what is te appropriate response. If we weren't there, we can't say whether the right call has been made. All we have to go on, is learner's own feelings in the matter. And the vibe I get, learner, is that you are glad that your son is getting what seems to be the right help and that charging him wouldn't have necessarily achieved anything constructive for him.
You've done the right thing in getting your daughter to a place where she can be safe. But you do still seem to have some concerns for your own safety, at least so far as wanting tips on how to better get out of a situation like this should it happen again.
Several things worry me about this:
1) You COULD choose to study the techniques used by Houdini, and become an escape expert. But if he did this again and you got out of his knots, this would only up the ante. You being able to escape, is not the answer. However, I do understand why you want this knowledge - you don't ever want to be in such a helpless condition again, this is part of your own recovery, to make yourself safe in your own mind. But frankly, the best way for you to feel empowered once more, is to get to the root of the trouble - find out why he did this, and fix it. I suspect you feel that so far, you're not there yet.
2) He knew you didn't want him to do this, plus as he was doing this you make it clear you didn't enjoy it, didn't want it and that it was wrong, but he kept going. He went back and forth, he seemed comfortable with what he was doing to you in the face of your continued requests for him to stop. You were crying, he didn't want to hear it, so he gagged you - that is NOT the response of someone who just wants to see what it would be like to watch someone he's tied up, for a game. That is when it went a long way away from ever being a game. He was getting some other bizarre "kick" out of doing this, and I think it goes way, way beyond Obsessive Compulsive Disorder (OCD).
I do think getting the alarm is a really good idea. But I think, for peace of mind and to regain your own sense of control of the situation, you need belts and braces. So get te alarm, wear it UNDER your clothing (so he won't see it obviously and remember to remove it). At the same time, set up a daily (or twice daily) alarm system with a friend or even the local police. A lot of neighbourhoods have this sort of thing, for elderly folk maybe, or frail. They arrange a signal, such as a phone call to a friend at a set time, or opening the curtains in a certain way. The phone call needs to be made at the same time and to te same person, so that if the call doesn't come, they will alert someone to go check on you to see if you're alright. YOu can also put signals in place in a similarway. The signal can be a positive signal, so if he's behaving oddly you open the blinds in a particular way, for example. Or a negative signal, so opening the blinds is what you normally do, but your failure to do this alerts someone.
Talk to the local shelters, they will have tips. Also talk to the police, see what ideas they have. Talk to orgnaisations tat deal with the frail aged. We have a system here called Neighbourhood Watch, they have ideas like this.
YOu may never need any of this, it migt all be completely unnecessary. But if it gives you peace of mind to put it in place, then it is worth any inconvenience. And I think that is what you're wanting here - peace of mind.
I had a really rough time during pregnancy with difficult child 3, during his delivery, and afterwards. There were a number of problems all contributing, including the worst bushfires in over a hundred years. For years afterwards, the sight of fires on TV (or in reality) or documentaries (or even news stories) dealing with either bushfires, or childbirth, would have my in floods of panicked tears. I had to find my own way of dealing with it. Part of my own methods were what I would do if I was ever in that situation again. I had to role-play it over and over, until I had rewritten events to a happier and more empowered conclusion. THis, despite the fact that I had made darn sure I would never, ever have another baby and so would never have a chance of being in that same situaiton, ever again.
Sometimes it doesn't matter how sure you are that you are now safe. You still want to know even more, how to regain your sense of empowerment.
And you always will have to consider - have we finally stopped him? Or not?
Only you can answer that one, we shouldn't try to second-guess.
Stay safe. Sorry you went through this. It is so hard sometimes, when our children hurt us.
Marg