Ten-code - Wikipedia

Ten-codes, or 10-codes, are used in two-way voice radio communication as numeric codewords for frequently used messages. They originated in the United States law enforcement community before World War II. There is no universal, official set of 10-codes, and the meanings of a particular 10-code can vary between one jurisdiction and another: a code meaning "I have the suspect in custody" in one state can mean "Send an ambulance" in a second state and have yet another meaning in a third.

The following is a sample of commonly used 10-codes, submitted for purposes of illustration. It is common for a 10-code to have numeric gaps.

10-1 Poor reception
10-2 Good reception
10-4 Message received
10-5 Relay this information to ___.
10-6 Busy
10-7 Out of service
10-8 In service
10-9 Please repeat your message
10-13 Civilians present and listening
10-15 Enroute to station with suspect
10-19 Return to station
10-20 Specify location/My location is ___.
10-21 Place a phone call to ___.
10-22 Disregard
10-23 Stand by on this frequency
10-33 Emergency traffic follows. Hold routine messages.
10-34 Frequency open (cancels 10-33)
10-39 False alarm, premises was occupied
10-40 False alarm, no activity, premises appears secure
10-41 Begin watch
10-42 End watch
10-45 Fueling vehicle
10-49 Enroute to assignment
10-60 Specify time complainant called
10-97 Arrival at assignment location
10-98 Departing assignment location