I have a factory alarm and I was wondering if I could make it more sensitive.

Factory Alarm or alarm installed at the dealer?
Anyway there should be a module that I would say is tiewrapped to your steering column. That is your motion sensor. Somewhere on it should be some type of screw, whether it be a screwdriver type or knurled finger type screw. You should be able to adjust the sensitivity to your liking. There should be a red LED that's lights up when it is triggered.
Hope this helps.

Its a factory alarm.

I may be wrong, but I don't think Toyota makes a factory alarm only keyless entry. They usually have tech's that install them on the lot. In Ca. they do anyways because I know a coupla of the installers.
Anyway, Like a said before, you should be able to find something under the dash that is either connnected to the steering column or to the firewall that has a sensitivity adjustment. In the old days they had them attched to the firewall inside the engine compartment , but I think they often died a quick death in there. Check and see if there is something underneath the dash.