Being a Locksmith Surry Hills area, I often work in terrace houses with sash windows. The best lock i have found for these is the Whitco Multibolt which can not only lock windows closed, but also lock a window open a few inches for ventilation. This is great for upstairs windows where children could potentially fall from an open window.
The locking pin requires a second hole drilled for the open position locking.
What's the difference between a Deadbolt and a Deadlatch