The short answer is that smoke alarms are not usually wired together based on a fixed distance between each unit. What matters most is that they are installed in the right locations for coverage and then interconnected correctly so that all the alarms sound when one detects smoke. In a typical home, that means one alarm inside or near every sleeping area, one on each level, and additional alarms in hallways or large open areas as needed. If your home has long hallways or multiple rooms, the placement should follow the building layout rather than a strict measurement like “every 20 feet.”
If you are asking how far apart the devices themselves should be on the wiring run, the answer is usually determined by the home’s floor plan, the electrical circuit design, and the manufacturer’s instructions. Hardwired smoke alarms are commonly interconnected with a dedicated interconnect wire, and all units on that group should be compatible. You do not space them evenly just for the sake of wiring. Instead, you place them where they can best detect smoke early and where they meet code requirements for coverage. In many homes, that means one in each bedroom, one outside each sleeping area, and at least one on every level, including the basement if it is used.
If you are working from code guidance, the exact rules can vary by location, so it is smart to check your local building or fire code. Some places require alarms within a certain distance of sleeping rooms, while others have specific rules for ceiling height, hallway length, and placement near kitchens or bathrooms. Even when the code is not very specific about spacing between alarms, it often is specific about where they should and should not go. For example, you usually do not want a smoke alarm too close to a kitchen or bathroom because cooking steam and shower humidity can cause nuisance alarms.
For installation, follow the manufacturer’s instructions exactly, because that is what inspectors and code officials will care about if there is ever a question. Also make sure all alarms in the house are the same type if they are being interconnected. Some homes use a mix of hardwired alarms with battery backup, and some newer units include voice or smart features, but they still need to be compatible if they are tied together.
If you want the safest practical approach, think coverage first, wiring second. Put the alarms where smoke is most likely to be detected early, then wire them together so any alarm triggers the whole house. If you are unsure about the layout, it is worth having a licensed electrician or local inspector look at it before you finish the install.
