Welcome back to our discussion on home automation safety! In our previous entry, we established our safety goals and outlined the system requirements needed to achieve these goals. Today, we’ll be exploring the safety mechanisms (SM) that underpin the system, ensuring it runs efficiently and securely.

In this entry, we will illustrate how these safety mechanisms help fulfill our safety goals. We will consider two components as examples: the Door Monitoring Component and the System Monitoring Component.

Door Monitoring Component

This component helps ensure that unauthorized access to the house is prevented. It uses inputs from door contact and occupancy sensors to monitor the status of external doors relative to the occupancy status of the house.

The following safety mechanisms are implemented:

1. External Door Monitoring in Absence (SM_DMC_1): This mechanism sends a level 2 notification when any external doors are open during the house’s absence, sleep, or home alone occupancy status.

2. External Door Open Duration Monitoring (SM_DMC_2): This mechanism sends a level 2 notification if any external door is open for longer than a predefined timeout interval.

3. Occupancy-based External Door Locking (SM_DMC_3): This mechanism sends a level 3 notification and schedules a door lock action if feasible when any external doors are unlocked when everyone is asleep or has left the house.

4. Maintenance of Door Sensors (SM_DMC_4): This mechanism schedules maintenance action for the user when a predefined period for door sensor maintenance has elapsed.

These mechanisms help ensure that external doors are locked when necessary, and alerts are given when doors are open for too long, providing an extra layer of security for the occupants.

System Monitoring Component

The System Monitoring Component is responsible for maintaining the overall health of the home automation system. It uses various inputs, including sensor and actuator status data, system health data, power supply status, and network connectivity information.

Several safety mechanisms are incorporated into this component:

1. Sensor/Actuator Monitoring (SM_SMC_1a, SM_SMC_1b, SM_SMC_1c): These mechanisms monitor sensor and actuator outputs, timeouts, and battery levels. They trigger notifications when anomalies are detected, prompting users to take appropriate actions.

2. System Update Reminder (SM_SMC_2): This mechanism sends a level 3 notification whenever there is a system update available.

3. Power Failure Management (SM_SMC_3): This mechanism sends a level 3 notification during power outages, provided a UPS is installed and functioning.

4. System Resource Usage Monitoring (SM_SMC_4a, SM_SMC_4b, SM_SMC_4c, SM_SMC_4d): These mechanisms monitor CPU usage, RAM usage, disk space, and hardware temperature. They send a level 3 notification whenever these resources exceed their respective thresholds.

5. Network Connectivity and Performance Monitoring (SM_SMC_4e, SM_SMC_4f, SM_SMC_4g, SM_SMC_4h, SM_SMC_4i): These mechanisms monitor the Ethernet link status, local network connectivity, internet access, internet latency, and packet loss. They send a level 3 notification whenever the network parameters deviate from their normal operational thresholds.

By continuously monitoring the system health and network connectivity, these safety mechanisms ensure that the home automation system functions reliably and efficiently.

Please note that these are just examples. A comprehensive list of all components, safety mechanisms, and the safety goals they address is available in the documentation found in our repository.