© Provided by Interesting ThingsGive your pet the freedom to come and go as they please.

The earliest pet doors were apparently just holes cut in the side of barns, which were an attempt to lure wild cats in so they could hunt the rats and mice and stop them from feasting on the grain or flour inside. But things have got a lot more sophisticated since then. Here are a few things worth bearing in mind before you buy...

© Provided by Interesting ThingsDesigned for use inside the house, this chew-proof set-up includes an 8-inch square lockable aperture so small animals can get through, but only when you want them to.

First things first, work out what sort of pet door you need. Does it need to sit in an external wall, or door, or do you actually need an internal one, that will allow you to restrict access to certain areas at certain times of the day? Internal gates are a bit like the sort of baby gates that you might fix at the top of a flight of stairs to prevent children falling down them, but some come with lockable pet doors in them which mean that you can decide that, for example, your pets can't go upstairs overnight. Just make sure they're high enough that they can't be jumped over!

© Provided by Interesting ThingsAn animal access panel that can be semi-permanently fitted, with no lasting damage, into the mechanism of picture windows opening onto a balcony or garden.

Obviously check the size of your pet and the size of the door, but if you're looking for a pet gate that will work in an external wall or door, also check what sort of material you're going to need to make a hole in, as that can affect the type of door you need to purchase. For example, there are kits that allow you to put a panel with a pet frame into a sliding glass door, without damaging the original fittings, but do check that this won't invalidate any home insurance claim in the event of a break-in.

© Provided by Interesting ThingsFor siding, stucco and brick constructions, this extendable frame can accommodate panels that are anywhere from 4 3/4 - 7 ¼ inches thick, with extension kits available. Comes in three different lengths.

Decide how secure you want your pet door to be. Even the simplest pet doors tend to have rudimentary locking devices that mean that they can be shut to prevent your animals going out, but if you're worried about pets that aren't yours sneaking into your house, it's possible to get electric doors that will only open to pets who have a matching collar, or whose microchip matches.

For siding, stucco and brick constructions, this extendable frame can accommodate panels that are anywhere from 4 3/4 - 7 ¼ inches thick, with extension kits available. Comes in three different lengths.

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