You can buy a motion sensor alarm for his bedroom door. Or some jingle bells, if he sleeps with the door closed.
He shares a room with both his sisters. I can't see any way having two exhausted kids added to the equation is going to help.
Stormbride, I sympathize with your frustration at the difficulties inherent in creating a safe environment for a kid who is having serious boundary issues. It is WORK. It's time-consuming, and frustrating, and has to be combined with more time-consuming, exhausting supervision. While he may not realize it, and while you wish he wasn't, your ds is asking you in the clearest possible way for a lot of direct supervision. You can sign him up for whatever energy-burning thing you want - it will probably be good for him, he'll love it, and he'll continue to seek attention from you in any way he can. The best, safest, soundest choice in front of you is to give him that attention.
Okay - so I send my daughters away for the day? I cannot even describe to you the level of attention he requires. It is NOT POSSIBLE for me to give it to him, and still look after my other children, do even basic housework (and believe me - it's basic), etc. In any case, I'm not physically capable of that level of supervision. I can't go running up and down stairs, chasing him around, etc. all day. My knees hurt. My back gives out (sacroiliac joint). And, I simply don't have the energy. I can't walk fast enough. I can't keep going long enough. I'm crashed by noon some days.
You know he can force you to pay attention - he just has to do something wildly unsafe. You are all better off if he gets your attention without having to resort to reckless extremities first. I hear that you're exhausted, and I know what I'm suggesting is difficult, and I really do sympathize.
He doesn't get attention. He gets yelled at and sent to his room, in isolation. If I keep him around when he does these things, it gets ugly.
I also sympathize with the feelings of your other children, who were so scared they had to lock themselves in a room and call you. They shouldn't have to live like that. You can't give in to exhaustion.
I can't give in to exhaustion. Well, isn't that nice. So, I'm not allowed to be human, and will drop dead by the time he's a teenager, because I "can't give in to exhaustion"? That's pretty much what I'm looking at. I haven't gone more than two weeks without getting sick in years - my body is done. I feel like I'm 80. Are you going to tell an old woman that she "can't give in to old age", too? I can remember functioning on 20 hours of sleep a week - for at least a year - and not being this exhausted.
Who can help you? Dad, grandparents, local agencies?
My dad is an alcoholic, who I haven't talked to, except on Father's Day (because I had to drop off his taxes, as I'd had them on my desk for months, and he's facing jail time) in over a year. My mom and stepdad are working themselves to death to maintain the small company that's paying her mortgage...and helping out with my sister's kids, as needed, which is way more necessary than my situation. (Yes - I'm serious. They've had CPS involved twice, and my nephew is profoundly gifted and is on the autism spectrum. His behavioural issues are a lot like ds2's, only more extreme, and more frequent.)
I have no friends who live nearby. I don't trust my neighbours, with good reason. Only one of them is home during the day, anyway, and she has a six month old. Local agencies? What kind of agencies?