Isn't this getting a little silly? If you can't get into the bathroom from your side, it means someone else is occupying. If you can get in, you lock the other door after yours.

This is why hall bathrooms are FAR superior to problem prone J&Js. Redesign the baths. And take a look to see the other poor design inflicted on the house by your drafts person.

Some after-the-fact house modifications don't lend themselves to anything but a J&J. I too could use a synchronized lock on 2 doors. If you see anything available in the US I'd be interested.

Wondering if you ever found a solution for this?

I would like to know if there's any other solutions in the market too... my old house has a jack and jill bathroom and it's the main bathroom (1.5 baths only). I wish there's a solution... I thought about making that J&J bathroom into 2 small bathrooms but I found out it's very expensive. I wonder if there's a better solution to solve this J&J problem...

Did anyone find a system that works? We are not able to redesign the bath to NOT be a Jack/jill.

what about adding smart deadbolts with an alexa or google home speaker in the bathroom? you could tell your smart speaker to lock or unlocked both doors. It would be less than 400 bucks.

I think Joseph's comment above is silly because it forgets the main problem with Jack & Jill bathrooms. The issue is that someone leaves the bathroom through one door, and forgets to unlock the other door, thereby not allowing anyone else to enter. It's the whole reason for the synchronized lock request.

I've been looking into this too. There are some high-end products available, but I think you need to decide how much the J&J lock problem is worth for your situation. In some cases it may make a lot of sense. I suspect there may be some DIY solutions using various off-the-shelf "smart home" components, but I haven't come across those yet.

well thought out, and least expensive starting at AUS$542:

http://www.alianelectronics.com.au/sm108b-door-interlock-system.html

USA product -- over US $2,000

(I love that the variation of this product is the "man trap". Hope they ship the right one!!)

https://dortronics.com/wp-content/uploads/4300-Communication-Bathroom.pdf

UK product - currently £1,845

https://www.hoyles.com/advanced-shared-bathroom-solution-kit-2-door-version.html