[genefitz]

Okay, first off, what year is your Aveo?
Second, if your horn does work, do you see the parking lights flash once when you lock, twice when you unlock?
Third, does the alarm work? (try opening your trunk while the doors are locked)

My 08 Aveo only honks once when I lock (arm the alarm) the doors. It does not honk when I unlock the doors.

All that said. If your car is less than 3 years old, or has less that 36,000 miles, and you have not fooled with the alarm system (added or taken from), the car should still be under the original bumper to bumper. They shouldn't charge you a penny to check out the alarm.
If the horn works, at las I recall, ALL Aveo alarm systems run through the horn, it should only give a short honk to let you know it is armed. And your lights should blink once to tell you it is armed, and twice to tell you it is disarmed. If neither your horn or lights are letting you know that your system is armed or disarmed, then you should check out the power to your alarm module, most likely the alarm is not working. This could be a fuse or an open in the power or ground.
If your alarm IS working, and your lights are flashing, then you will most likely have an alarm module failure. If your lights are blinking with no horn alarm, and the alarm is working but only showing flashing lights, and no audible horn alarm, then it would be an open in the out-leads from the alarm module to your horn (note: the horn may still work, just the connection from the horn to the alarm module itself may be broken.)
Last case, if your car is not under warranty, if you try all these ideas and come to no resolution, spend the $100 to get it checked. I would anyway. If the dealership does the repair, you get some guarantee on the work.
Just a thought (or 12)