In you have sliding aluminium windows and you want to make them more secure, you may want to install or make a lock. There are several different options. Take a look:
Sliding Bar Lock
A sliding bar lock fits into the track of your aluminium window, and it has a small bar that slips over the window that slides open. When you attach this lock to the track of your aluminium window, it makes it impossible to slide open the window. Additionally, the bar that extends over that window makes it impossible for a thief to try to push the window out of the track from the bottom. This is the only option that has that feature.
Thumb Screw Locks
A thumb screw lock also fits into the track and blocks the other window from sliding into the track. To engage this lock, simply tighten the thumbscrews, and to open it, release the thumbs screws. The lock stays in the track whether you are using it or not, and it slides across the track as you open and close the window. To ensure it doesn't damage the finish on your aluminium window, look for a lock that has been lined with non-marring rubber or plastic.
If you don't want to risk losing the thumb screws or if you have dexterity issues that may make turning them difficult, you may want to opt for a levered lock. This operates on the same principle as the thumb screw lock, but it features a lever that triggers a small latch inside the lock to block the track.
A keyed lock blocks the track of the window, but it can only be opened by a key. If you need to control who opens or closes the lock, or if you simply prefer the additional sense of security associated with a key, this may be the lock for you. However, there's always a risk of losing the key, and manually removing the lock, if the key is lost, may bend the window frame.
You can also make your own makeshift lock using a dowel. Find a dowel at a craft or hardware store that fits in the track of your aluminium window. Then, place the dowel in the track to prevent the window from opening. So that the dowel looks cohesive with the window, paint it the same colour as your window frame.