The constant beeping from your Notifier FSP-851 smoke detector could indicate a few potential issues. Firstly, check if the device is properly installed and secured in place. Ensure there are no loose connections or debris interfering with its functionality. Additionally, verify if the detector’s power source is stable and adequate. Sometimes, fluctuations or interruptions in power can trigger false alarms. If the issue persists, it’s advisable to consult the device’s user manual for specific troubleshooting steps or contact a certified technician for further assistance.