difference between these 553T alarms?

The one with the 2-button remote is at least a couple of years old. It is definitely better to have the lock and unlock buttons separate......that way, even if you can't see your car, you will know if you are arming or disarming.....with one button for both functions, you have to be near the car to know what you are doing. -The newer one has one extra auxillary output (for trunk, neons, etcetera) -The newer one has the above-mentioned 4-button remotes. -The newer one has an updated antenna design---the range is probably better. -If you look at the relay pack, you'll see that the newer unit has one more relay---this is the second ignition output. If you buy the older one and your car has two ignition wires (most do), you'll need to add another relay yourself. I would contact the seller of the cheaper unit and ask him just what you're getting------the auction does say that the unit is brand new-----he might simply be using an outdated picture. If you don't get a good answer, just pay the extra $25 or whatever it is for the newer one; it'll be worth it.