I Think Fawad Elahi is right- you will have to first select the area you are interested in. Also it may be based on your budget and tools available. Also select which sensors you want to make use of for inturrupt.
You have to select from-
1. Mechatronics (where you may work on robots, motor control based on sensor input etc)
2. Communication (from 433MHz communication to GSM to zigbee, all open for you. You can send data from the sensors even GPS data from GPS module.)
3. Security systems where sensors array and based on sensor inturrput you may decide what to do, would be a nice project.