Which statement best describes the historical signaling format used in older alarm systems?

• A. It uses 4 x 2 relay information
• B. It uses IP signaling
• C. It uses cellular networks
• D. It uses telephone dialer codes

Answer: (A)

Old alarm systems often used a simple relay-based signaling method, encoding status with a set of relays that each have two states (energized or not). Four relays give you four binary bits, which can represent multiple conditions, and this setup is described as providing 4 x 2 relay information. It’s a practical, robust way to convey different alarm events over the copper lines available at the time, long before digital networks or wireless signaling. The other options point to later technologies (IP signaling, cellular) or to dialing-based methods, which aren’t what older, relay-driven systems used to describe their signaling format.