## 3 The Proposed Scheme
### System Architecture  
1. Client (C): The customer needs a security service from the security company. He/she carries a smartphone with the security company's application that enables them to get the notification when an event happens at his/her house. 2. IoT main controller (IMC): A controller that is installed in a client's house, and connects to every Internet of Things (IoT) device in the house, e.g., camera, alarm sensors, magnetic contact, switched, motion detection devices, and fire detection devices. All security events are controlled by the IoT main controller. Each sensor can be triggered by an event that triggers the security problem with the client's house; for example, a thief breaking into the house, or a fire incident. 3. Security control center (SCC): This is the security company's control center that can monitor the client's home security situation. If there is an event triggered by the client's house, the control center's staff needs to notify a security guard to take action and go to the client's house to solve the problem. 4. Security guard (SG): He/she drives a car and carries a smartphone. He/she needs to take action when they receive the task/notification from the SCC to solve the security problem in the first scene. 5. Blockchain center (BCC): This is the blockchain that records the event. When an event from the client's house is triggered, the BCC creates a record with an event ID, and sends an active notification to the SCC; every message reply to the event needs to be chained with the event ID. Figure 1: System framework of the proposed scheme. 6. Official agency (OA): This is the third-party official agency. The client can ask to prove the contract and event from the BCC. The official agency has the right to prove that is there any problem when executing the contract from the security company. All staff in the security company (including security control center staff, and the security guard) needs to register an account from the BCC to get a unique ID. When the client needs a security service from the security company, after the contract is signed, the client, the client's house with the IoT main controller, and the IoT sensors that are inside the house also need to register to the BCC to get a unique ID, a public key, and a private key pair. Figure 1 presents the scenarios which are triggered by an event by some IoT devices (IoT) of the client's house. 1. A thief breaks into the client's house or a fire incident happens. The client's house security system (with sensors) is triggered to the IMC, and the IMC notifies the SCC with a new event ID. 2. The SCC's staff will connect and check the recorded video from the digital video recorder (DVR) before and after the occurrence event time manually. Every client's house needs to install a digital video recorder (DVR) and connect it with multiple cameras to capture the critical area. Those devices are classified as IoT devices. If there are no abnormal movements or objects (e.g., human break-in, or fire) in the video, then that means it is a false alarm. The SCC's staff checks if it is a false alarm or not and confirms it. Then, SCC searches for available SGs that are nearby the event client's house. If there is an event at the client's house, a notification will be sent to the specific SG. 3. If SG accepts the task, then the SG sends a confirmation message to SCC. 4. SCC generates and sends the confirmation message to BCC and chains the confirmation record in the BCC. 5. The SG goes to the incident scene and solves the security event. 6. After the event is solved, the security guard reports the detailed records and sends the report to the SCC. 7. SCC sends the record to BCC and chains the report to BCC. 8. The client receives the latest status notification from the SCC. 9. If the client does not satisfy the service of the security company, the client can propose an arbitration request to the official agency (arbiter). 10.