A lot can happen in less than 30 seconds. Usually, it's terrible destructive acts that damage lives for really long times. Car accidents leap to mind.
But along with the devastation so short a time can bring, there are also things that, if we took those 30 seconds, work to save lives.
Testing your smoke alarm and changing the batteries in it can be done in 30 seconds if you have the batteries with you when you check it. Quick and a lifesaver.
Click that seatbelt. In high speed crashes, seatbelts save lives. Not so much in fender benders. Be sure you're wearing it properly - if the lap portion rides high, like over your belly instead of across your hips, you might injure your spine in a high speed crash. If the shoulder part crosses your neck, even in a low speed crash, you could injure or even break your neck. In a high speed crash, it could decapitate you. Wear your seatbelt properly. It takes less than 30 seconds to click it.
Lock doors. Your house, your car, your office, your shed. Once it's a habit, it takes way less than 30 seconds both to lock and unlock the doors. A locked door can save you from a serial killer (like Richard Trenton Chase), a casual robber, a carjacker.
Have your blood pressure checked. Most pharmacies have the machines and they will work in about 30 seconds. Do any follow up you need to do - heart health lengthens your life.
If you or your child or a friend receive a hard knock on the head during play, call a time out. Stop playing. We now know that multiple head injuries can cause lasting damage even if it's not apparent at the time of the injury. Better to endure jeers and taunts and live a long healthy life than to push your way through. It's just a game. Don't risk your future health and life for a game. save that for the important things in life.
Put on a helmet when riding a wheeled vehicle. I'm tempted to include riding lawn mowers on this. I've seen a few neighbors take some nasty spills on their mowers because their yards are too small for a riding mower but they just had to have one. Definitely do it for motorcycles and those open little sport ATVs. Bicycles, I'm kind of torn about. I never wore one as a child and still don't, but then, I also don't try to go fast on a bicycle and don't wear straps tying my feet to the pedals. If you go faster than a casual walking pace (my typical biking speed), I'd wear the helmet. There's a huge difference between road rash and traumatic brain injury.
Take the keys away from friends or loved ones who are not sober - either because of alcohol or drugs. Don't try to reason with someone under the influence, they'll often get argumentative. In my experience if you ask to play with the keys, they'll hand them over. Play with the keys for a bit, when they get distracted, pocket the keys and don't mention them again. Most of the time, they'll forget.
If you're walking after dark along a street that doesn't have a sidewalk, make yourself visible to cars. A cellphone can be flipped open to make you more visible. A flashlight is better, reflective tape or a reflective scarf better still. I drive to work before sunrise most of the year, and during winter,it's dark both ways. There's nothing more terrifying than realizing there's a person in the road and you're about to hit them because they are wearing all dark clothes and are walking on the wrong side of the road with their black hoodie up. If you have light skin or hair, it won't bee seen until (sometimes) too late. Make yourself visible if you're walking down a dark street.
I'm sure there are plenty of other 30 second things you can do to keep yourself and your friends and family safe. These are just off the top of my head.