@GeorgeWhite This is provided for in Article 4D(3): the office of first filing issues a certified copy of the prior application, and the applicant files this copy with the office of later filing. Again, the certified copy is included in the file wrapper of the later application, and therefore becomes accessible to the public even if the office of first filing never publishes the prior application.

Actually, one paragraph in the European Patent Office's Guidelines for Examination sternly warns Examiners against accidentally disclosing the contents of unpublished patent applications when searching for prior art. So your concern is definitely valid!

@DonQuiKong neat edit, your answer is easier to understand now.

@Haider Not quite. You say your idea uses an accelerometer. So the accelerometer is an essential feature of your invention (in the sense that your invention wouldn't work without one). So the accelerometer must be recited in your independent claim(s). What DonQuiKong says is that it does not matter that the accelerometer is known by itself, as long as your claimed invention as a whole is novel and inventive.

I must also add that whenever you are amending your application, you must make sure that you are not introducing any new matter. This can be a surprisingly subtle exercise, and some jurisdictions are very unforgiving in this respect (in particular the European Patent Office).

I totally agree with @EricShain. All we can say in abstract is that all of the claims have to be novel, inventive, and have industrial applicability, and that (as you probably know) you achieve this by making sure that each independent claim meets these criteria. Anything beyond that is fact- (and often jurisdiction-) specific. A patent attorney is best placed to advise you.