magic mouse switches to different mac

Most of the time I work at home with MacBook Pro and I also have an iMac for my personal use. Sometimes my MacBook's Magic Mouse switches to iMac just like that. I'm working and I wonder why the mouse suddenly doesn't work and then I see it's interacting with iMac on the other side of the room. Also the touchpad starts working with the iMac. That's annoying. And the iMac's mouse starts interacting with MacBook Pro. When I put the iMac to sleep, after a little struggle, the mouse starts working with MacBook again. How can I prevent the mouse switching between Macs without my consent.