Recently, young thieves have begun to access 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. 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.
Patio doors are another high risk access to the home.
The simple solution is to block the moveable patio door from being pryed up and out of its track by putting screws into the frame above the door where it sits when it is in its closed position. Regardless of the bar installed, it must be kept tight at all times to continue to be effective. During the summer months, a lockable chain gate can in many instances provide a very slight amount of extra security, by preventing thieves from driving directly up to your cottage. The best advise I can give is simply not to leave anything in the cottage which you can't afford to lose. Alarm systems are only useful if there is a neighbour present to hear the horn.