NIXA, Mo. -

The threat of hearing sirens and the need to take cover at a moment's notice is driving many homeowners to storm shelter show rooms to check out their options.

"You think a lot about it. The closer it comes the more you think about it," said Rodger Iversen.

Sunday's storms were a wake up call for the Iversens who aren't too confident in their existing shelter space.

"We have a cellar but the cellar was built 80 years ago and it was hand dug and the rocks used for the cellar walls were piled up so it's not very safe and not really good," Iversen explained.

And they're not alone. Many customers are on a waiting lists because the demand for shelters is so high right now.

"Every time we have a tornado outbreak, especially the closer to Springfield people get motivated emotionally and they come in and all want to buy storm shelters," said Jeff Olsen, Owner of Missouri Storm Shelters.

Business owners say customers have also gotten more educated about the products because they've learned from disasters in neighboring counties.

"We are getting more and more people coming in and requesting the National Storm Shelter seal of quality verification on the shelters. We have been noticing that they really want that quality verification that way they know the shelters are built and installed properly," said Olsen.

Depending on size and style units can range from $2,900 to $6,5000. It's a lot of money for most people to pay "just in case" but some customers see a value that extends beyond just stormy days.

"We can use it for both locking up our valuables like guns paperwork and jewelry and of course the obvious reasons which are the tornado threats," said Iversen.

Experts say the best time to get a safe room is in the fall or winter where the demand is a little lower so you can have more time to practice your emergency plan before tornado season. Also FEMA has residential grants and rebates available through its website to help with some of the costs.