What Is a 10-21a Police Code? 10-21a Police Code

The 10-21a police code meaning for the police forces is Advise Home I Will Return At [ETA – Estimated Time of Arrival].

If you’ve ever come across the term 10-21a police code and wondered what it means, you’re not alone. So, what is 10-21a police code? The 10-21a police code is a specific communication signal used by law enforcement officers, and it translates to “Advise Home I Will Return At [ETA – Estimated Time of Arrival].” This code allows officers to efficiently relay their return time to dispatch or relevant contacts at home base.

Breaking Down the 10-21a Police Code

The 10-21a police code is a variation of the more general 10-21 police code, which simply means “Call by Telephone.” The added “a” in 10-21a customizes the message further, offering more specific information related to personal or administrative communication.

The full message conveyed with code 10-21a is:
“Advise Home I Will Return At [ETA].”
This allows an officer to quickly notify headquarters or a dispatcher of their estimated time of arrival, maintaining smooth communication during operations.

History of Police Ten Codes

Police codes, often referred to as Ten Codes, originated in 1937 as part of the APCO (Association of Public-Safety Communications Officials) Ten Signals. These radio communication codes were designed to simplify and standardize law enforcement communication across different jurisdictions. They reduce confusion, save time, and improve clarity in fast-paced or emergency situations.

When and why the 10-21a Police Code Is Used

Law enforcement personnel use 10-21a primarily during shift changes, post-assignment reports, or when checking in with their department or loved ones. It’s a practical way to keep communication brief but informative, especially during active duty or mobile patrols.

What Is 10-21a Police Code?

The 10-21a police code is a shorthand message used by law enforcement to indicate “Advise Home I Will Return At [Estimated Time of Arrival].” It’s a variant of the 10-21 code, which means “Call by Telephone.” These radio codes, introduced in 1937 as part of APCO’s Ten Signals, help officers maintain effective, quick, and accurate communication—an essential part of police operations.

Whether you’re studying law enforcement communication or simply curious about police radio lingo, understanding the 10-21a police code offers insight into how officers stay connected and organized while on duty.

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All Police Codes—Your Ultimate Resource for Police Radio Codes Across the United States

Welcome to All Police Codes, your comprehensive and trusted source for police codes used throughout the United States. Whether you’re a civilian enthusiast, emergency services supporter, or someone simply curious about how law enforcement communicates, our goal is to provide you with in-depth information and a clear understanding of police radio codes—especially the 10-21a police code and hundreds of other vital codes used daily by emergency responders.

Our expertly curated police codes guide is designed to be an educational hub, allowing you to discover the meaning and usage of various law enforcement radio codes, including the widely searched 10-21a police code, which plays a crucial role in police communication systems. At All Police Codes, we don’t just list the codes—we explain their history, significance, and real-world applications.

The 10-21a Police Code and Its Role in Law Enforcement Communication

The 10-21a police code is just one of many 10-codes used in police radio communication, enabling officers and dispatchers to convey information quickly and efficiently. This specific code is often associated with returning a phone call, but its exact meaning may vary slightly depending on jurisdiction.

These radio signals are essential tools that help first responders relay critical information during high-pressure situations. With the use of police scanners, enthusiasts can even listen in and learn how these codes are used in real-time. Understanding the 10-21a police code and others gives you deeper insight into the structured, high-speed communication networks that keep our communities safe.

Decades of Research and Passion for Police Communication Systems

Our team at All Police Codes has been researching and following police communication systems and radio signals for many years. We are passionate about helping people understand the language used by law enforcement, firefighters, and other emergency personnel across the country. These codes are more than numbers—they’re tools that allow emergency services to act swiftly, coordinate responses, and save lives.

Police codes, including the 10-series, were originally developed between 1937 and 1940 to standardize and simplify communication over radio channels. Later, in 1974, the Association of Public-Safety Communications Officials-International (APCO) expanded and refined these codes to meet the growing demands of public safety communications.

In fact, APCO’s involvement dates back even further. In June 1935, APCO proposed Morse code brevity codes in The APCO Bulletin, which were initially based on the U.S. Navy’s procedural symbols. While those early procedures were designed for Morse code rather than voice transmissions, they laid the foundation for the voice-based radio codes we use today.

Commonly Used Police Radio Codes—Understanding the Language of Emergency Response

One of the most commonly used police radio codes is 10-7, which means “out of service.” When an officer completes their shift, they may also use the 10-42 code, meaning “ending tour of duty.” These codes not only serve operational purposes but also carry symbolic weight, especially in ceremonies honoring fallen officers.

From simple updates like 10-4 (acknowledgement) to urgent alerts like 10-33 (emergency, all units stand by), police codes serve as an essential language for coordination, discretion, and rapid response.

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Whether you’re here to understand the 10-21a police code, decode a message you heard on a scanner, or simply dive into the fascinating world of emergency communication, All Police Codes is here to guide you. Bookmark our site, share it with fellow enthusiasts, and keep learning the language that helps protect and serve our communities every day.

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