A bell jar containing an alarm buzzer inside of it can be pumped out. When the buzzer is in a vacuum, it will not sound because there is no air for the waves to travel through. As the valve is opened and air pressure returns inside the bell jar, the alarm will sound again.
Set up time
10 minutes (5 minutes to pump the bell jar)
Physics and Science Concepts
Plug in the pump and attach the clear tube of the pump to the valve. Turn the switch on the power supply to ascertain that the alarm is working properly. Then, pump out the air inside the bell jar. It will take about 5 minutes to obtain a low enough air pressure so that the alarm will not sound. Turn the alarm on and slowly open the valve, allowing the air pressure in the bell jar to increase. The sound of the alarm will also gradually increase.
A glass jar containing a vacuum can be extremely hazardous if broken.