With regards to house clearing, the one thing I've preached for years is...
Never clear a house by yourself.
If you go looking for trouble,
you're likely to find plenty of it.
Night lights are easily one of the cheapest things you can invest in. A nightlight in a bathroom will cast enough light out the door to illuminate part of the hallway.
If you have a two-story house, lights strategically placed on the ground floor to cast shadows visible from the top of the stairs will aid in locating intruders too.
Remember, though, that if intruders have managed to get inside, they are going to do one of two things. Listen for sounds of awakened residents OR rush through the house to locate and neutralize the occupants quickly. Having a dog or two may cause the former type to flee but only delay the latter.
If you think you hear a stealth-intruder inside, the noise you make getting out of bed and acquiring your firearm and flashlight may alert him. Also remember you won't be wearing your glasses. If Mr. Murphy is unhappy with you, you'll find one arm is half asleep, your eyes blurred by "sleep", perhaps the urge to cough and clear your throat. Even if not, your heart will be racing and the drums in your ears keeping time with your heart will diminish your hearing. Know that fear makes breathing harder and it sounds like Darth Vader breathing in your ear. When you try to call out in your best John Wayne or Bogart tough-guy voice, don't be surprised if you instead sound more like Don Knotts going through puberty. And if you've turned the heat down to 55* while you sleep it won't be very long before your body starts to shiver in the cold.
If you're lucky and your house has remote lighting capability, turning on kitchen/livingroom lights will typically startle anyone inside and encourage them to leave. But you can't be sure they did leave or that ALL of them left. But those lights might buy you time to secure your family in single, defensible room.
Besides night lights,
First Alert makes simple battery powered alarm units that can be sticky-taped to a window or door (I've used velcro). These alarms will give you some warning before they get inside.