## 3 Beacon-Based Hazard Alarm System Design
### Detailed Design of the Components
#### 3.3.1 Beacon-Based Distance Monitoring
In Estimote Cloud, another IoT application was designed to create a notification and send it to the FCM topic based on the data received from the LTE beacon. As shown in Figure 3, the system uses the \"Post\" method to create both the data and notification within FCM and send them to the mobile applications. The two fields within the data correspond to the district and the identification number of the beacon sensor to locate the hazard source. The notification is the words shown on the screen of the Android application, and the title and body text of the notification instruct the user about the hazard and the appropriate actions to be taken to mitigate the safety risks. #### 3.3.3 Android Application

The Android application is designed to receive the notification and data from FCM and warn the user by auditory signals and a notification message. The application includes an FCM configuration and dependencies to enable the FCM platform to work with the application for this function. The mobile application is connected with the FCM platform by subscribing to the topic explained above, which allows a mobile phone to receive what Estimote Cloud has sent to the FCM platform. When a hazard alarm message arrives, the application produces an auditory alarm and a message that can contain information about the type of hazard and how to mitigate the risk. Figure 4 shows the user interface and the screen when a notification arrives on a mobile phone. When the user opens the application, it is automatically subscribed to the FCM topic, which means that it is ready to get notifications and data from the FCM platform, and the system is activated, as shown in Figure 4. During the operation of the application, when the receiver beacon sensor gets close enough to the sender beacon sensor located near a hazard, the mobile phone keeps receiving notifications and sounding alarms, as shown in Figure 4a. The alarm system continuously sends the alarm notifications until the user pushes the \"understood\" button (Figure 4b), making the application unsubscribe from the particular topic. Figure 3: Server connection detail. ## 4 Field Experiment

### Experiment Design Concept

As the next step, a field experiment was conducted to investigate the impact of different deployments of the beacon signal sending devices on the hazard notification reception on the user's mobile phone. The question to be addressed by this experiment was the following: \"What should be the locations of the Bluetooth sensors for the workers to receive individualized hazard notifications most effectively?\" In this question, the word \"effectively\" is combinatory of several conditions the system would need to satisfy, such as the timing and range of alarm notifications. Depending on the type of hazards, the timing of the notification's reception can be critical for worker safety. If exposure to the hazard instantly poses a great threat to the worker's health and safety, such as live electrical wires, it would be ideal for the worker to recognize the hazard before entering or nearing the workspace. On the other hand, some hazards, such as dust and ergonomic hazards, are dangerous only when exposed to the hazard for a while. In this case, it may not be a significant problem if the hazard notification is received shortly after the worker enters the workspace. In addition, some hazards, such as a poisonous chemical spill or gaseous hazardous materials, can affect workers over a wide area, and therefore, every worker in the affected area needs to be notified of the hazard. On the other hand, some hazards are exposed to the worker only when the worker contacts an object or the structure, such as collisions or falling. In this case, only the workers carrying out a task near the hazardous object or work environment need to be notified of the hazard. When a sensor-based hazard alarm system is designed, alarm fatigue also needs to be seriously considered.