This is a Southern Freetail Bat, also known as the Little Mastiff Bat, one of the more common micro-bats in north-east Victoria. In other parts of the world this group of bats is known as snub-nosed bats. The snub-nosed, or mastiff-look, is obvious (compare the bat to the dog) and if you look closely you can see that more than half the tail length is ‘free’, that is, not contained within the tail membrane, as is the case for many other micro-bats (look here), hence the term free-tail.
Like all micro-bats, Little Mastiff Bats are insectivorous and play an important role in controlling insect numbers. Its worth making them welcome around your house and garden; they live in tree hollows and cracks, and inside roofs! Although they can see, their eyes are small; they fly and catch insects using echolocation, a type of radar. Most nights we hear squeaks and high-pitched squabbling coming from the roof cavity in our house, sure sign that our little insect-eaters are waking up and getting ready for their nocturnal adventures. Occasionally, one of them squeezes through the wrong crack and finds a way into the house.
In fact, what we call Southern Freetail Bats (Mormopterus planiceps) are most likely a group of very closely related species that are very hard to tell apart. Here are pictures of two male Southern Freetail Bats that came inside, which we then had to catch to get them back outside.