AFAIK, there's nothing out there. I recently thought the MM had failed and ordered a replacement, the new one still doesn't have terminals for adding a device. So soldering a 2-wire lead for a contact sensor is -unfortunately- the way to go. Video of hack is in the thread linked below. BTW, my first one failed because ants decided to fill it with eggs. 2 days of blasting with contact cleaner and drying it in the sun and it started working fine. I suggest applying some petroleum jelly to the standpipe.