I'm assuming the screens are removable from the outside vs inside? I would need to see pics but you should be able to screw in small brackets along the sides to secure the screen. I don't think secured screens are an issue during a fire since a human could easily break thru screen windows.

The following link has some clips that may work. A few screw into the frame and others use pressure screws to hold the clip in place.
Your other option is to call a storefront that specializes in windows & doors and see if they have anything in stock that you can use.

Here is a link that might be useful: screen clips

Not your question but I wanted to mention they make pet proof screening which works really good! I re-screened my front and back patio door with it. My one cat climbs up it (about 1/2 way) and it holds her weight without tearing the screening.

I keep one window open all summer for them to sit in. I just popped a couple of nails in to hold it secure and we've been fine.

I HAD the same problem and HAD the same concern with my screens. The vinyl screen was held to the frame by a tiny rubber gasket that the cats could (and did) easily push out with minimal effort. Vinyl screening or cat-proof screening wouldn't have mattered, since the rubber gasket was the part that gave way. After more than a decade suffering with no air conditioning and windows I couldn't risk opening more than 2" all summer, I FINALLY found a solution! It's not pretty, but it works like a charm. Baby gates! A portable, expandable baby gate across the inside of each window frame allows me to open the windows fully, get great air flow, and still keep the cats safely inside. A really determined cat can still stick a paw through the baby gate and snag the screen - maybe even tear the screen or push it out - but the cat can't get through the baby gate to escape. Like I said, it's not a pretty solution, but it is effective, and it's given me back a livable house during the hot summer season.

Laurie

GREAT idea!
thanks for sharing it

Thanks for the suggestions! I was thinking of something similar to what Laurie said but instead I think I'll try some gardening lattice and velcro, lol. All of my windows are all on the same wall in each room so I think I could cover them with a 3 foot long and one foot high lattice piece that I can secure to the wall with velcro when I want to use it and take it down when I don't. They have pretty white designs that I think would actually look nice in my house while letting the air through and providing a little extra support that the cats can't get through. I'm still thinking about it though!

I think lattice would work just fine, though you may have to repaint where you attach the velcro to the window frame. That stick-on velcro may damage certain surfaces when you remove it. Or you may have the opposite problem. I've used stick-on velcro that hasn't done a very good job of staying stuck to the surface I stuck it onto, so you'd want to make sure it stayed really secure on the window frame and the lattice.

Laurie

Here's a pic of a baby gate in one of my windows. The nice thing about baby gates is that they are fully adjustable for different window widths, so they can quickly be moved from window to window, if desired.