In addition to the DECT telephones, handheld radios are used for communication purposes. They serve as backup at important points in case the DECT network fails and are also used for 1-n communication.
You may find a radio at your shift. In this case please make sure that the battery is not empty, the correct channel is set and the device is loud enough for you to understand. Communication always starts with an initialisation phase with callsigns. Because most likley noone knows that you are the security-angel at the door, you should use "Entrance Glass Hall" as your callsign, not your real name or your nickname. For example: "Entrance glass hall for Secu" - "Secu hears".
You can find more details on radio traffic at https://howto.c3roc.de.