they do come with a stock alarm, that said the stock alarm is pretty much just a blinking red light that keeps honest people honest. I have tried to get the alarm to go off and it pretty much takes someone jogging into the car to set it off. I think Subaru offers a high sensitivity upgrade for the 13. I think the part number is H7110FG000. It provides a secondary shock sensor on the driver side dash panel that is very sensitive to vibration. Im pretty sure it also has an adjustment so you can tune it to be more sensative.
There's always viper aftermarket units, I'm a huge fan of their products but the installs are not something that I recommend doing yourself. Ive been doing installs foryears and its still more of a hassle than a 6 pack and a pizza will compensate for. Last I checked you can remote start, control AC and even setup a NO KEY proximity entry with the new models.
Just my .02cents.
Slow is Smooth > Smooth is Fast