Older model Challenger garage door openers were originally equipped with varying types of radio receivers and remote controls.
 
If you have a remote control for your garage door opener, look on it for the following information: Make (Multi Code, Liftmaster, Chamberlain, Tec Key).  Then click on that manufacturer name on the menu on the left side of the page.  You can then look at the various models and see if anything looks like the one you have.  If you find one that looks like your current remote control, be sure to look at the "Compatible with these Models" section to determine if it is compatible with your garage door opener.  Manufacturers often change things, such as transmission frequency, over the years and it may or may not be compatible.
 
If you cannot determine what type you have, we recommend that you install a new radio receiver/transmitter.  This radio gear features the new rolling code technology for added security.  The one we recommend is our Universal Remote Control Kit (this includes the new receiver and one remote control).  It is quick and easy to install.  Since it is an add-on receiver, you can continue to use any remote controls and keypads that are currently working with your garage door opener. You can add additional remote controls at any time and also a wireless keyless entry keypad if you desire. 
Click here for more information -  Universal Remote Control Kit