In New York State, police officers are considered on duty 24/7 and are required by department policy and State Penal Law to uphold the law at all times. Their powers of authority do not end when they end their shift, which is probably why they are seen as desirable employees for other unofficial security jobs. However, one cannot simply take on a second job without officially requesting in writing to their department supervisor working that off duty job.
Peace officers have more limited authority, arrest powers equal only to that of the average citizen, and only within the scope of their special duties, such as corrections, park police, hospital security etc... When off duty the department doesn't require, nor desire, Peace officers to act as police officers because they don't have the extended training in Penal Law, arrest procedures and all the mountains of paperwork that must be filed correctly, that is required of police officers. One better be very familiar with the Penal Code on the use of force, especially deadly physical force, or one just might end up in jail.