1. Hook up a photo cell and an LED. Have the LED shine brighter (using PWM) when there is more light and dimmer when there is less light.
2. Hook up a Tilt Sensor and the speaker. Have activating of the tilt sensor make an alarm go off.
3. Use the reed switch and the magnet to make a sound when the magnet is close.
4. Hook up the piezo element and use it to play a tune after someone knocks.