Any window covering an area used as a sitting room or bedroom should be equipped with window bars mounted on the inside that can be opened. A key for any associated padlock should be hung out of sight and below the window, preferably with a decal clearly indicating its use. A replacement key should be put away in a safe place in case of loss of the original.

If more than one window is padlocked, all padlocks should be on the same key. Intruders also break into homes through windows left open on second floors of the home. This is a potential risk if the window is accessible above a verandah or garage roof. Keep them locked at all times when they are not in use. Block sliding windows with tight fitting pieces of wood, and (where possible) with screws above the window in the track to keep the window from being lifted out.

In some cases, where the window is a double slider, the outside sliding half of the window must be actually screwed shut to prevent it being opened. This will restrict you to opening the window using only the other inside portion of it, which you can then block, with a tight fitting stick in the inside track.

-- Tips courtesy of HomeAdvisor.com