I did a bunch of research on this. Here is what I learned. If you have keyless entry and an engine immobilizer (standard on V8s), you have the alarm. It might not be activated if you did not have it listed on your window sticker, but it is there. Many techs and dealers don't even know it is there, but it is.
My buddy who is a Lexus tech activated mine with the Toyota Techstream scanner in a few minutes. He did not know it could be done until I convinced him to try. We then took a co-workers to his buddy who is a Toyota tech and activated his. His buddy did not know how to do it, but another tech there did. It does not have to have a Glass Break Sensor (GBS) or hood switch present.
If you can make the horn sound and lights flash by pushing the panic button on the remote, the alarm is there.
Some dealers will charge you to activate it, some will not, many will tell you it can't be done. Better yet, buy a tech a six-pack or slip then $20.
Here is the install PDF for the glass break sensor. On pages 10-17 it explains how to activate the alarm with the scanner. Those direction might help you convince the tech/service department that it can be done.
Good luck with the activation for those that don't have it active.
If you want to read more there is a discussion
here.