App developer's business question.

A friend and I have a great idea for an app.

Now here is what we need to find out - (And we are using a hypothetical to not give away our good idea)

Let's say it is sometime in the past, 20xx, rather than 2016.

And we have a great idea for an app that would let your smart phone determine how many calories are being burned, how many steps you have taken, yr heart rate etc.

No one else that we know of has done this yet (it is after all, the year 20xx)

So do we first patent our idea? (I don't think patents are allowed, but figure folks here would know more than me.)

Also, how do we find out if someone else is doing this, and maybe so far along in the process
that we shouldn't bother? With patents a person in Calif can simply go down to an office in Sunnyvale, or even on line, and research their good idea, but with apps, how do you know what is being worked on?

Thanks to any and all replies.