Somebody Else's Problem field, or SEP, is a cheap, easy, and staggeringly useful way of safely protecting something from unwanted eyes. It can run almost indefinitely on a torch (flashlight)/9 volt battery, and is able to do so because it utilises a person's natural tendency to ignore things they don't easily accept, like, for example, aliens at a cricket match. Any object around which an S.E.P. is applied will cease to be noticed, because any problems one may have understanding it (and therefore accepting its existence) become Somebody Else's. An object becomes not so much invisible as unnoticed.
A perfect example of this would be a ship covered in an SEP field at a cricket match. A starship taking the appearance of a large pink elephant is ideal, because you can see it, but because it is so inconceivable, your mind can't accept it. Therefore it can't exist, thus ignoring it comes naturally.
A S.E.P. can work in much the same way in dangerous or uninhabitable environments. Any problem which may present itself to a person inside an S.E.P. (such as not being able to breathe, due to a lack of atmosphere) will become Somebody Else's.
An S.E.P. can be seen if caught by surprise, or out of the corner of one's eye.
Slartibartfast's ship, Bistromath, is covered in an SEP field.
Appearances
The S.E.P. is found in Chapter 3 of Adams' Life, The Universe and Everything