If that is a Honda unit it may have been installed by a previous owner. If a Honda dealer would have installed it the parts would have been located in different parts of the vehicle. See if you can pull out the black box and see if it has any name on it, it should have an antenna lead on it if it is a Honda unit and it should have a glass sensor sensitivity switch. The Honda system should have a disarm switch under dash. Compare the parts and wiring in the link below and see if everything is still in tact.

http://www.handa-accessories.com/S2000/s2ksecurity.pdf