Ten-Four Day

What the day is

Ten-Four Day is observed on October 4, for the obvious reason: written as 10-4, the date is the best known of the radio ten-codes. It honors radio operators, from police and emergency dispatchers to truckers and amateur radio enthusiasts.

"Ten-four" means message received and understood. It does not mean agreement, a distinction that matters more on a radio than in the films that borrowed the phrase.

Origin and background

The ten-codes were developed for American police radio around 1937, credited to Charles Hopper of the Illinois State Police. Early two-way radios needed a moment to key up before transmitting, and the first syllable of a message was often clipped. Prefixing everything with "ten" gave the transmitter time to engage and made the meaningful part survive. Brevity mattered too, since channels were shared and airtime was scarce.

The codes reached the public through citizens band radio. CB boomed in the United States in the 1970s, propelled by the oil crisis and the national speed limit, and truckers used it to report traffic, weather and police locations. A run of films and hit records in the same decade pushed CB slang into ordinary speech, which is why people who have never touched a radio still say ten-four.

Professionally, the codes are in retreat. Ten-code meanings were never standardized nationally, so the same number meant different things in neighboring jurisdictions, which becomes dangerous when agencies respond to an incident together. After major multi-agency emergencies exposed that problem, federal guidance pushed responders toward plain language, and many departments have dropped the codes entirely.

How to take part

• Thank a dispatcher. Emergency communications work is stressful, invisible and rarely acknowledged.
• Look into amateur radio. Getting licensed is straightforward, and operators still provide emergency communications when other networks fail.
• Keep a battery or hand-crank radio at home. When cell service goes down in a storm, broadcast radio is what still works.
• Learn the phonetic alphabet. Alpha, Bravo, Charlie is genuinely useful the next time you spell your name over a bad phone line.