Humans frequently need to construct a huge number of buildings for occupants in large cities to work or live in a highly developed civilization; people who live in the same building or same area are defined as a community. A thief stealing items, a burglary, fire hazards, flood hazards, earthquakes, emergency aid, abnormal gas leakage, strange behavior, falling in a building, fainting in a building, and other incidents all threaten the community’s safety. Therefore, we proposed a blockchain-based community safety security system that is combined with IoT devices. In the proposed scheme, we designed multiple phases to process the alarm triggered by IoT devices. IoT devices can be set up in two types areas: private and public areas. Both types of IoT devices’ alarms have different process flow for the response and records checking phase. All records are saved in the Blockchain Center to assure the data can be verified and cannot be forged. During the communication between sender and receiver, we implemented some security methods to prevent message repudiation, prevent transmission intercept, prevent replay attacks, and ensure data integrity. We also implemented a clarifying mechanism to ensure that all system participants can have confidence in the system’s processing methods. The proposed scheme can be used in communities to improve community safety and prevent unnecessary conflicts.