“People don’t think of wiring as a danger, because it’s out of sight behind walls,” says Lorraine Carli of the NFPA. But electrical fires have accounted for more than 50,000 home blazes a year, plus $1.5 billion in property damage. And seemingly innocuous acts, like driving screws into a wall to hang a mirror, can easily pierce wiring. One good fix: Replace circuit breakers with arc-fault circuit interrupters (found in hardware stores for about $30. These safeguards detect dangerous electrical arcs—abnormal sparks that signal bad insulation or loose connections—and stop them before they start a fire.