I worked as a security guard in the property for nearly 4 years. The general manager saw me smoking in the square the other day and immediately fired me. Can I apply for compensation?

Your description is relatively simple. If your company stipulates that smoking during working hours is a serious violation of the rules and regulations of the employer, and it is publicized, it is effective. If you violate the regulations, the employer can terminate the labor relationship with you. If the unit does not have the above provisions, and your behavior is also a serious violation of discipline, then the unit is not allowed to dismiss you casually, otherwise you need to pay economic compensation. If the employer wants to dismiss the employee, it needs to notify the employee in writing 30 days in advance before it can dismiss, and it needs to pay economic compensation. If it is considered illegal for the unit to terminate the labor contract, it may report to the labor inspection department and demand to continue to perform the labor contract or terminate the labor contract, but require the unit to pay economic compensation. You can also directly file a labor arbitration to safeguard your legitimate rights and interests (refer to People's Republic of China (PRC) Labor Contract Law).