In extent number three protection, what is the specified sound detection level?

• A. Sound detection below 65 dB
• B. Sound detection above 100 dB
• C. No sound detection is used
• D. Sound detection exactly at 70 dB

Answer: (A)

The important idea is how a sound detector is tuned to balance sensitivity with avoiding false alarms. For extent number three protection, the target is that sound detection happens when ambient noise is below 65 dB. This keeps the detector responsive to genuine intrusion sounds without being triggered by normal, everyday noise that often stays around or above that level. Decibels scale logarithmically, and around 65 dB you’re at a level similar to normal conversation with some background hum; keeping the threshold below that helps the system distinguish real events from ordinary noise. If the setting were much higher, it could miss quieter but important intrusion sounds; if you had no sound detection at all, the system wouldn’t protect at all; and choosing an exact 70 dB is overly precise and impractical given real-world variations.