Which emergency equipment uses a volume knob during its preflight check on the CRJ700?

The megaphone is the emergency equipment that uses a volume knob during its preflight check on the CRJ700. A megaphone is designed to amplify a person's voice so that it can be heard over significant distances or loud environments, which is crucial in emergencies to communicate effectively with passengers and crew.

Having a volume knob allows the user to adjust the sound level according to the situation. During the preflight check, ensuring that the megaphone is operational and the volume is appropriately set is essential for its effective use in an emergency scenario.

The other pieces of equipment do not require volume adjustment in the same way. The PBE (Protective Breathing Equipment) is focused on providing breathing protection, the AED (Automated External Defibrillator) is designed to deliver electrical shocks to restore normal heart rhythm, and the FAK (First Aid Kit) contains medical supplies for immediate care but does not involve audio amplification. Therefore, the presence of a volume knob specifically indicates the megaphone's role during its preflight checks.