Hello! I understand your X-Sense combo smoke and carbon monoxide (CO) detector alarm is sounding, and pressing the silence button doesn't stop it, plus there’s no message on the device. Let’s try to get this sorted out.

First, to clarify a couple of things and better guide you:
- When the alarm sounds, is it a continuous loud alarm or a repetitive beeping/chirping?
- Have you noticed any other indicators on the device like blinking lights or unusual behavior?
- Do you know if the batteries are recently changed or if the device is hardwired with a battery backup?
- Is this device interconnected with others, meaning does the alarm trigger in multiple units simultaneously?

Often, persistent alarms with no message can be caused by a low battery, dust inside the sensor, or a fault in the device itself.

Here’s a step-by-step plan to troubleshoot:

1. Check Battery and Power
- If your device is battery-powered or has battery backup, try replacing the batteries with fresh ones. Low battery can cause the alarm to sound continuously or chirp repeatedly without messages.
- If it’s hardwired, ensure it’s properly powered and consider resetting the circuit breaker for the unit.

2. Silence/Troubleshoot the Alarm
- Press and hold the silence/reset button for about 15-20 seconds. Some X-Sense models use a long press to reset or silence the alarm.
- If this doesn’t work, try pressing the test button four times quickly and then pressing and holding it until it beeps to reset (this is a known reset method for X-Sense alarms)9.

3. Clean the Device
- Dust or humidity can cause false alarms. Use compressed air to blow dust out from the sensor openings. Make sure the environment is dry and well ventilated8.
- After cleaning, test the alarm again.

4. Check for Faults or Sensor Issues
- Sometimes, if the CO sensor detects unsafe levels, the alarm won’t silence until the environment is safe. Try ventilating the room well with fresh air and see if the alarm stops
- If the alarm persists with no apparent cause and no message indicating CO or smoke presence, the unit may have developed a fault.

5. Full Device Reset
- Power off the device by removing batteries and/or disconnecting power. Wait about 5 minutes to clear any electronic errors.
- Reinstall power and batteries, then try the reset steps again.

If after these steps the alarm still will not silence and no message is displayed, the device might be malfunctioning internally. In that case, I suggest contacting X-Sense support directly or considering a replacement. For immediate safety, if you suspect CO exposure, evacuate and call emergency services.

Would you like me to guide you through any of these steps in detail or help find X-Sense support contact info? How does this sound so far?