Definition
In a remote indicating compass system, the direction-sensing device is the magnetic-field-detecting unit (typically a flux valve) mounted in a part of the aircraft with minimal magnetic interference, such as a wingtip or vertical stabilizer. It senses the horizontal component of the Earth's magnetic field and transmits that directional information electrically to a separate indicator in the cockpit.
Plain English
It is the part of the aircraft's compass system that actually feels which way is north. It sits out in a quiet spot on the airframe, away from electrical noise, and sends the heading information to the display in front of the pilot.
Context Anchor
Seen in discussions of remote indicating compass systems, where the sensing part may be mounted away from metal or electrical equipment that could affect a compass reading.
Why Pilots Care
It permits the sensing element to be mounted away from cockpit magnetic interference while still providing accurate heading to the pilot.
Intuition Check
Do not assume the direction-sensing device is the cockpit display itself. In this context, it is the part that detects direction; another part may show that direction to the pilot.
Example Sentence 1
The flux valve in the left wingtip serves as the direction-sensing device for the slaved heading indicator.
Example Sentence 2
If the direction-sensing device fails, the remote compass indicator will no longer receive accurate heading information.