Buy 2 of these Nest Protect Smoke & Carbon Monoxide Alarms and your total drops from $258 to $199 in your cart at HomeDepot.com. Shipping is free. This gets you each alarm for only $99.50 each, the lowest price we found anywhere by $31. These alarms are highly reviewed and come in a wired (120v) or battery version. It has extra perks, like sending a message to your phone if the alarm goes off or batteries run low, or giving you a "Heads Up" alert so you can avoid the full alarm going off during a non-emergency. Sales tax is charged in most states.