Depending on what kind of door it is (is it wood or steel?) you could mount a second deadbolt in the door further down, out of reach of the window. Drilling the new holes in the door would be the most difficult, if you don't have experience doing such a thing. You can get a jig kit to drill the holes.
As someone pointed out in another comment, you can rekey the new lock to match the old ones (make sure it's the same brand lock, so it uses the same type of key).
A double-keyed deadbolt is an option, but it might be against local code. This is never a great option as it also limits your options as far as operating the lock from the inside, you'll always need a key to get out. It's easy to assume you'll always have a key on hand, but in an emergency (i.e. in a fire) that might not be as easy as you assume (this is the typical justification for this type of lock being against code).
Another option, consider a swing bar guard and mount it low enough on the door to be out of reach.