Remind your friends to test their smoke alarms monthly! It's something that can very easily slip your mind, so it helps if you and your friends encourage each other to test them at the same time.
Smoke alarms need to be replaced after 10 years. This is also hard to keep track of, so it might behove you to ask your friends about their old smoke alarms.
If you or your friends are unable to climb a ladder to test your alarm, there are now alarms that can be tested using a TV remote.
Every household needs a CO detector on every level. Carbon Monoxide is the “silent killer” for a reason: It has no smell or taste, and the symptoms of CO poisoning are very easily passed off as a minor illness (headache and fatigue).
If your CO detector goes off, immediately move yourself and your guests to a 'fresh air location', either outdoors or next to an open window, and call 9-1-1.