Which transmission methods have been used for alarm signaling systems historically and currently?

• A. Telephone lines only
• B. Telephone lines initially; now radio, Internet, and cellular networks
• C. Satellite only
• D. Fiber optic only

Answer: (B)

Alarm signaling has moved from a single wired path to multiple pathways to improve reliability. In the past, alarm signals were sent over traditional telephone lines, which worked but left the system vulnerable if the line was cut or powered down. Today, many systems use several options: wireless radio links, cellular networks, and Internet-based signaling over IP. These paths can be used alone or together in redundant configurations, so an alert can still reach the monitoring center even if one path fails. Satellite signaling exists but isn’t the standard primary method for most alarms, and fiber optic is part of the broader communications landscape rather than the sole method used. So the best description is that signaling started with telephone lines and now includes radio, Internet, and cellular networks.