Smart smoke and CO detectors can be a big investment. Replacing every unit in an average two-story home can easily cost $600 - $1000. Keep in mind that most states do require interconnected smoke alarms in the home, and the rest will in the near future. So if you're nearing the 10-year replacement period on your current alarms -- and excited about smart tech -- switching to smart detectors puts you ahead of the curve.If smart tech isn't your thing, traditional hardwired alarms fulfill that requirement for a fraction of the cost.