Amazon has X-Sense Portable Carbon Monoxide Detector w/ Digital Display (XC0C-SR) for $11.99. Shipping is free w/ Prime or on $35+.

X-Sense USA via Walmart has X-Sense Portable Carbon Monoxide Detector w/ Digital Display (XC0C-SR) for $11.99. Shipping is free w / Walmart+ (free 30-Day Trial) or on orders of $35+

Thanks to Deal Hunter doublehelix for sharing this deal.

Features:

• 10-Year Lifespan: Protect your loved ones from the silent threat of carbon monoxide for an entire decade with this reliable 10-year CO sensor; powered by replaceable AA batteries that last 3 years
• Travel-Friendly Design: Slip this compact CO detector into your bag or suitcase for extra peace of mind when you travel; measuring only 3.0 × 5.6 × 1.3 in (75 × 142 × 32 mm) and using AA batteries, this convenient device can be taken in carry-on or on trips abroad
• Versatile Placement Options: This CO detector's flexible design allows you to place it on any flat surface, such as a desk, bookshelf, or bedside table; screws are also included to mount it on the wall
• Intuitive to Use: Easily use this alarm even in urgent situations thanks to its simple, size-differentiated buttons; enjoy reliable access to critical functions like checking the peak CO levels or testing/silencing the alarm
• Easy to Understand: See the current CO level on a clear display; a tri-color LED tells you the alarm's status at a glance: red for alarm, yellow for fault or low battery, and green for working normally