The development of the 10-codes began in 1937, at a time when police radio channels were limited, to reduce use of speech on the radio. Credit for inventing the codes goes to Charles "Charlie" Hopper. He was the Communications Director at the Illinois State Police, District 10, located in Pesotum, Illinois. Hopper was involved in radio for many years and saw a need to abbreviate radio transmissions on State Police bands. Experienced radio operators know that the first syllable of a transmission is frequently not going to be understood, but is a necessary part of "tuning in"; hence preceding every code with "ten" allows a better chance of understanding the critical portion. Also, the radios of the day were based on vacuum tubes, with a small motor-generator, called a dynamotor, used to generate the high voltage (300–600 volts, depending on the type of radio) needed to operate the transmitter, and the dynamotor took 1/10 to 1/4 of a second to "spin up". The officers were trained to push the microphone button, then wait a moment before talking, but sometimes they would forget; preceding every code with "ten-" gave the radio transmitter time to come up to full power.

Ten-codes were later adapted for use by CB radio enthusiasts before its pop culture explosion in the late 1970s. The tremendous popularity of the 1975 Convoy song by C.W. McCall depicting droll conversation among CB-communicating truckers put several phrases, such as 10-4 for "understood" and what's your twenty? (10-20) for "where are you?" into common and enduring use in American English. The song was followed by a 1978 movie Convoy, which further entrenched the use of ten-codes in casual conversation.

Related codes

In addition, many agencies mingle various codes, especially those that used radio dispatch before the ten-codes were developed. For instance, the Los Angeles Police Department, which pioneered law enforcement radio communications, largely set the standard for law enforcement communications in California. Dispatchers began using California Penal Code sections in their broadcasts in the 1940s, and these code numbers are still used today, instead of the corresponding ten-code. The best-known include:

* "187" – Homicide
* "211" – Armed Robbery
* "415" – Disturbance
* "417" – Man or woman with a gun
* "502" – Intoxicated Driver
* "5150" – Mentally Ill Person

Generally these are given as two sets of numbers – "One Eighty-Seven" or "Fifty-One Fifty" – with a few exceptions such as "459" – Burglary, which is given as "Four-Five-Nine." The well-known "420" for marijuana, however, originates from neither.

The California Highway Patrol uses eleven-codes, and the Port Authority Police uses eight codes as part of their communication.

Ten-codes are generally avoided in services such as amateur radio where other existing standards (Q code and prosigns for Morse code) are already long established. Aviation and marine radio is better served by Q-code, as the ten-code phrase lists were designed primarily for local police tasks while Q-code provides specific abbreviations for concepts related to aviation, shipping, RTTY, radiotelegraph and amateur radio. In radiotelegraph operation, a Q code is often shorter (as ten-codes require transmission of three prefix characters: 1, 0, hyphen) and provides standardization of codes, essential in international and shortwave communication.

Police Scanner 10 Codes

10-0 Caution
10-1 Reception poor
10-2 Reception good
10-3 Stop transmitting
10-4 Message received, understood
10-5 Repay message
10-6 Change channel
10-7 Out of service
10-7A Out of service, home
10-7B Out of service, personal
10-8 In service
10-9 Repeat message
10-10 Off duty
10-10A Off duty, home
10-11 Identify frequency
10-12 Visitor(s) present
10-13 Weather and road advice
10-14 Citizen w/suspect
10-15 Prisoner in custody
10-16 Pick up prisoner
10-17 Request for gasoline
10-18 Equipment exchange
10-19 Return(ing) to station
10-20 Location
10-21 Telephone
10-21A Advise home I will return at:
10-22 Disregard last assignment
10-23 Stand by
10-24 Request car-to-car transmit
10-25 Do you have contact with:
10-26 Clear
10-27 D.D.L. report
10-28 Registration request
10-29 Check for wants
10-29F Subject wanted, felony
10-29H Hazard potential from subject
10-29M Subject wanted, Misdemeanor
10-29V Vehicle wanted
10-30 Doesn't conform to regulations
10-32 Drowning
10-33 Alarm sounding, audible
10-34 Assist at office
10-35 Time check
10-36 Confidential information
10-37 Identify operator
10-39 Can () come to the radio?
10-40 Is () available for phone call?
10-42 Check the welfare of/at:
10-43 Call a doctor
10-45 Condition of patient?
10-45A Good
10-45B Serious
10-45C Critical
10-45D Dead
10-49 Proceed to:
10-50 Under influence of drugs
10-51 Drunk
10-52 Resuscitator
10-53 Man down
10-54 Possible dead body
10-55 Coroner case
10-56 Suicide
10-56A Suicide attempt
10-57 Missing person
10-59 Security check
10-60 Lock-out
10-61 Miscellaneous public service
10-62 Meet a citizen
10-62A Take a report from a citizen
10-62B Civilian standby
10-63 Prepare to copy
10-64 Found property
10-66 Suspicious person
10-67 Person calling for help
10-68 Telephone for police
10-70 Prowler
10-71 Shooting
10-72 Gun involved
10-73 How do you receive?
10-79 Bomb threat
10-80 Explosion
10-86 Any radio traffic?
10-88 Assume post
10-91 Animal
10-91A Animal, stray
10-91B Animal, noisy
10-91C Animal, injured
10-91D Animal, dead
10-91E Animal, bite
10-91G Animal, pickup
10-91J Animal, pickup collect
10-91L Animal, leash law violation
10-91V Animal, vicious
10-95 Need ID tech unit
10-97 Arrived at scene
10-98 Available to assign

Police Scanner 1-37 Codes

Code 2 Urgent - no light or siren
Code 3 Use lights and siren
Code 4 No further assistance needed
Code 5 Stakeout
Code 6 Stay out of area
Code 7 Meal break
Code 8 Restroom break
Code 9 Summer uniform
Code 10 SWAT pre-call up
Code 11 SWAT Call up
Code 37 Subject/Property wanted

Police Scanner 11 Codes

11-10 Take report
11-24 Abandoned vehicle
11-25 Traffic hazard
11-26 Abandoned bicycle
11-27_10-27 W/driver held
11-28_10-28 W/driver held
11-40 Advise if ambulance needed
11-41 Ambulance needed
11-42 No ambulance needed
11-44 Deceased person (Coroner Req'd)
11-48 Furnish transportation
11-51 Escort
11-52 Funeral detail
11-54 Suspicious vehicle
11-55 Officer being followed by auto
11-56_11-55 W/dangerous persons
11-57 Unidentified auto at assignments
11-58 Radio monitored, use phone
11-59 Intensive attention: high hazard, business areas
11-60 Attack in high hazard area
11-65 Signal light out
11-66 Defective signal light
11-78 Aircraft accident
11-79 Accident - Ambulance sent
11-80 Accident - Major injuries
11-81 Accident - Minor injuries
11-82 Accident - No injuries
11-83 Accident - No detail
11-84 Direct traffic
11-85 Tow truck required
11-94 Pedestrian stop
11-95 Routine traffic stop
11-96 Checking suspicious vehicle
11-97 Time/security check on patrol
11-98 Meet:
11-99 Officer needs help!

Police Scanner Codes...

187 Homicide
207 Kidnapping
207A Kidnapping attempt
211 Robbery
211A Robbery alarm
211S Robbery alarm, silent
217 Assault with intent to murder
240 Assault
242 Battery
245 Assault with a deadly weapon
246 Shooting at inhabited dwelling
261 Rape
261A Attempted rape
273A Child neglect
273D Wife beating - Felony
288 Lewd conduct
311 Indecent exposure
314 Indecent exposure
374B Illegal dumping
390 Drunk
390D Drunk, unconscious
415 Disturbance
417 Person with a gun
417A Person with a knife
459 Burglary
459A Burglar alarm
459S Burglar alarm, silent
470 Forgery
480 Hit and run - Felony
481 Hit and run - Misdemeanor
484 Petty theft
487 Grand theft
488 Petty theft
502 Drunk Driving
503 Auto theft
504 Tampering with a vehicle
505 Reckless driving
507 Public nuisance
510 Speeding or racing vehicles
586 Illegal parking
594 Malicious mischief
595 Runaway car
604 Throwing missiles
647 Lewd conduct
653M Threatening phone calls

Police Scanner Codes...

Code Blue Bus/Cab in trouble
Code Red Varda Alarm activated
Code Purple Gang Activity
Medical / Fire Status Codes...
Code 10 Critical Trauma case
Code 20 Acute Trauma case
Code 30 Trauma case
Code 40 Serious case (IV started)
Code 50 Basic transport (not serious)
Code N Newsworthy event

Police Scanner Codes...

5150 Mental case
10851 Auto theft
10852 Tampering with vehicle
20001 Hit and run - Felony
20002 Hit and run - Misdemeanor
20007 Hit and run - Unattended
21958 Drunk pedestrian on roadway
22350 Speeding
22500 Illegal parking
23101 Drunk driving - injuries
23102 Drunk driving
23103 Reckless driver
23104 Reckless driver
23105 Driver under narcotics
23109 Racing
23110 Person throwing objects at
vehicles
23151 Drunk driving - injuries
23152 Drunk driver