The Mitsubishi Outlander is now in its third generation. It comes with keyless entry and factory immobiliser as a standard but lacks an alarm.
My recommendation is the Cobra AK4615 CAN-BUS upgrade alarm which works flawlessly with the Outlander.
It works with all models including the Outlander PHEV (Plug-in Hybrid Electric Vehicle).
Here are some photos of what the alarm looks like installed:
Here is how they look when back in the car:
Gen 2 Outlander 2006-2012
If you have the Older GEN 2 Outlander then the AK4615 is also a great option as shown below:
GEN 1 Outlander (Airtrek 2001-2008)
The Airtrek can also use the Cobra AK4615 in PLIP mode or a remote alarm.