avchecker:
…air duct detectors shall be tested or inspected annually to ensure that the device will sample the airstream…"
NFPA 72-2007 Chapter 10 (10.4.2.2 14g(4) )

"…Air pressure differential must be measured between the two openings falls within the specified operating range of the detector…"
NFPA-72 Chapter 10 (10.4.2.2 14g)

"Each air duct type smoke detector shall be inspected and tested to conform operability"
CAN/ULC-S536-05,5.7.4.4.1