What are the "10-codes"? Almost as many different codes exist as there are agencies using codes in radio transmission. The following are officially suggested by the Associated Public Safety Communications Officers (APCO): 10-1 Cannot understand your message 10-18 Urgent 10-2 Your signal is good 10-19 Contact ________ 10-3 Stop transmitting 10-20 Location ("Where you are") 10-4 Message received ("OK") 10-21 Call _______ by telephone 10-5 Relay information to ________ 10-22 Cancel last message 10-6 Station is busy 10-23 Arrived at scene 10-7 Out of service 10-24 Assignment completed 10-8 In service 10-25 Meet _______ 10-9 Repeat last message 10-26 Estimated time of arrival is _______ 10-10 Negative ("no") 10-27 Request for information on license 10-11 ________ in service 10-28 Request vehicle registration information 10-12 Stand by 10-29 Check records 10-13 Report ________ conditions 10-30 Use caution 10-14 Information 10-31 Pick up 10-15 Message delivered 10-32 Units requested ("send backup") 10-16 Reply to message 10-33 Emergency! Officer needs help 10-17 Enroute 10-34 Correct time