Window safety recommendations
It's not a window lock but a mesh in place of bars. http://www.amazon.com/KidCo-KID-S303-Kidco-Window-Guard/dp/B002H0JDPY
We use them in our house and are very happy with them and they aren't ugly like the bars.
We have these and I LOVE them. They are easy to remove so that you can open the window (if your window lifts from below you don't need to remove them at all), but they lock so that little hands can't unlock them. Highly recommend.