Breaking and entering through windows is less common than through doors because windows are less convenient and are more risky if glass is broken. Broken glass draws attention and may cause burglars injury, leaving DNA evidence behind.
Sneak in through a window left partially open for ventilation
Open a closed but unlocked window. That was easy.
Force open your window with a pry bar, popping weak latches
Smash the glass. They may do this even if it makes noise because your neighbours usually hesitate to call the police on the first loud sound heard.
Apply security film to glass. Realize that this only slows them down. See video below.
For basement windows, add interior window bars and ensure that you can still get out in case of fire.
Replace just the glass module with insulated laminated security glass designed to resist impacts. This is only recommended for casement style frames with strong multi-point locking mechanisms or non-operable window frames.
Replace the entire window, not just the glass, that is designed and tested to resist burglaries as a system. This would include insulated laminated security glass, reinforced frame, wall connections, hardware, and fillings. These look like regular windows on the outside but are very different internally. This is a great option if you need to replace old windows anyways.
Watch this before deciding choosing how to protect your glass patio doors and high risk windows. Some people may have a false sense of security after installing film.
Regardless of type, keep your windows locked. Burglars could simply check for unlocked or open windows and inconspicuously and quickly enter.