Nanites used to modify human brain

[Lurch666]

I borrowed a sci fi book over 15 years ago and would like to find it again.The basic story was set in the future where nanites are used all the time to modify a person's brain to accomplish tasks.The main character was a security guard and had modified his brain so he could go into an 'alert but asleep' status so he could do long shifts without getting bored.Anyway He gains the ability through the use of more nanites to change reality.The story was that every choice creates one or more reality's and he gained the ability to choose the reality he wanted.In the story he uses a watch battery as a coin and he keeps flipping it and as long as it always comes 'positive side' up he knows that he is still controlling to outcome of his reality.Ring any bells with anyone?I've done some internet searches for it but since I can't even remember the title or author I got nowhere.

[Mostlyharmless]

My memory is also going but it might be "Quarantine" by Greg Egan, which you should read even if it was not the book you wanted. You could look at the Wikipedia entry but it might be a slight spoiler.

[Lurch666]

That's spot on-checked the wiki(since I read the book before spoilers didn't matter) and it sounds correct so now I can order the book.can't thank you enough as I've wanted to re-read that book for years.YAY!