On a UL mercantile security system, a switched personal door shall not open more than how many inches without initiating an alarm?

• A. 1 inch
• B. 2 inches
• C. 3 inches
• D. 4 inches

Answer: (B)

The key idea is how door position is monitored. A switched personal door uses a door contact that signals the alarm panel whenever the door moves beyond a small, defined opening. For a UL mercantile installation, that threshold is set at two inches. If the door is opened more than two inches, the circuit triggers the alarm, capturing an actual security breach or a door left ajar.

This two-inch limit strikes a balance: it avoids false alarms from ordinary door movement, settling, or minor bumps, while still catching meaningful openings that could indicate unauthorized entry or a door being propped open. A smaller limit, like one inch, would be too sensitive and generate frequent nuisance alarms, whereas larger gaps—three or four inches—could allow someone to slip through without triggering promptly.