Combo smoke detector/carbon monoxide alarm detects two threats Electrochemical CO sensor alerts you to carbon monoxide danger Photoelectric sensor detects smoke while minimizing false alarms Battery-operated unit installs quickly and easily without an electrician，A single button tests the unit or silences the alarm. Low battery signal mute, quiets low battery signal for up to 8 hours ARRANTY AND SERVICE: Our products provide after-sales service. If you have any questions about our products, you can contact us, we will reply to you as soon as possible within 24 hours