Secure double-hung windows by inserting a key-operated lag screw through the sash, or replacing your existing latch with a key-operated lever.
Install screws in the upper tracks of sliding glass windows. The window should just clear the screw as it moves so there is no room to wiggle the window out of its tracks. You can also install a key-operated lock for added security.
Remove the operator crank from casement windows. For extra security, install a keyed lock on the sash rail.
Add keyed sliding bolt locks to basement windows, if they do not currently lock.
Replace your current windows with laminated-glass windows. Intruders have difficulty breaking through laminated glass because of the extra plastic or vinyl security layer that is sandwiched between the panes of glass.
Consider using tempered glass when replacing your windows. Tempered glass is up to 5 times stronger than regular glass, making it difficult for burglars to break.
Use wired glass for basement or less visible windows. The wires are visible, making it a less optimal choice for intruders.
Install locking gates have grilles mortared into the foundation of your home for extra security in high crime areas.