Ending today, Beach Camera via Rakuten offers the Nest Protect Smoke and CO Alarm 3-Pack for $327. Coupon code "SAVE15" cuts that to $279.65. With free shipping, that's the best price we could find by $47, although we saw it for $13 less in December. They feature a 120º field of view to 20 feet and work with the Nest app to send motion alerts.
You probably don't need a year's supply of toilet paper to survive an outbreak, but consider stocking up on these items.