Supposedly which direction you look depends on which part of your brain you are using. If you are remembering stuff, you look in a different direction to if you are inventing stuff.

For naive use it is not very reliable. One reason is that inventing stuff doesn't necessarily mean you are lying. Brains are complicated. For example, if I ask you how many chairs in your kitchen, you might remember it directly as a number, or you might imagine a little picture of your kitchen and then count the number of chairs in it. The counting phase could involve a different part of your brain to the remembering phase.

Another reason is that you really need to "calibrate" it because we are not all the same. For example, a left-handed person won't necessarily look in the same directions as a right-handed person. And of course, if you know the trick you can be trained to fake it out.

That said, I'm told it is a technique used by professional interrogators, eg against captured spies in the military. And it may be the kind of thing which people use subconscously. Don't try to fool your mother. She will have the calibration down pat.