The McAfee FailOpen Module enables traffic to pass through without interruption during maintenance and power outage. This active Fail-Open module constantly monitors Sensor state. It does this by sending a heartbeat packet through its ports. The heartbeat packet is sent through one of the monitoring ports and received through the other, indicating that the sensor is functioning normally. This modular expansion base offers three free slots and two hot-plug internal power supplies for uninterrupted usage.