Also of note is that Homelink requires a separate box for some older cars like my 2008 Toyota Avalon. I have a new Garage Door Opener and it refused to pair with my Avalon but worked fine with the BMW. I had to purchase a HomeLink Compatibility Bridge Kit and hook it up to the opener in order to get it to work with Avalon.
http://www.homelinkestore.com/Produc...ridge-Kit.html