Security, Access Control, and CCTV Systems
This domain blends physical security devices with the low voltage infrastructure that supports them. For access control, understand the components - reader, controller, electric strike or maglock, request-to-exit device, door position switch, and power supply - and the critical life safety rule that egress must never depend on the access system: fail-safe locks release on power loss and fire alarm, while fail-secure locks do not. Know why the REX device and the fire alarm interface are inspected, and why a maglock typically requires both.
For CCTV/IP video, know camera types, lens and field-of-view basics, resolution and bandwidth tradeoffs, and the importance of lighting and WDR. Understand PoE power budgets, NVR/VMS architecture, storage retention math, and cybersecurity basics such as changing default credentials and segmenting the camera network. For intrusion, know zone wiring, end-of-line resistor supervision, and the difference between normally open and normally closed circuits.
Traps: assuming a fail-secure lock is acceptable on a required egress door; forgetting that a door position switch and REX serve different purposes; confusing bandwidth with storage; and overlooking that camera placement for identification differs from detection. Another trap is treating a balanced line or supervised loop as optional - it is what makes tampering detectable.
Worked rule of thumb for storage: retention days × cameras × bitrate × 86400 ÷ 8 gives bytes; sanity-check the result against the NVR's usable (not raw) capacity and leave headroom for motion-based recording variability. For locks, always verify the door's egress classification before selecting hardware.