I keep keys in 2 key boxes in my office. Each key has a tag with a number. That way if a key is lost, it is # 25, no other ID.
Intrusion alarms are a problem, usually because of lack of maintenance. I prefer to have my own access code. That way the owner knows when we have been in and when we left. Each crew leader should have a phone number of the owner, a responsible employee, someone they can call if the alarm cannot be reset. The code and process need to be written down and in possession of the employee. I have one customer where I have my access number, the owners access number, and the employee's access number. Sometimes, because of lack of maintancence, the alarm still goes off. Just make sure all the lights are on, call dispatch. Give dispatch info on what company vehicle you have and where it is parked, your phone number, and keep working. If the cops show up, let them in, give them your ID and CCW permit. If the cops show up in an unmarked vehicle and not in uniform, do not let them in until you have called dispatch. Then next day visit your client and discuss how you are going to prevent the problem. Some jurisdictions charge enormous fees for unwanted alarms. If your people made a mistake, pay for it. if the codes were changed or inoperative, not your problem.