How does the iPhone 6 fingerprint software work while asleep?

I have the finger security software enabled on my iPhone. When I fall alseep, am I vulnerable to a potential third-party being able to place my thumb on the designated security pad (i.e. Home button) whilst I'm sound alseep?

I live with some highly untrustworthy people, and I store valuable financial data on my phone. I'm somewhat concerned that one night, when I'm sleeping, they may attempt to gain access to my phone by using my thumb.

Is the iPhone 3GS still usable/ worth it in 2015?

I'm thinking about getting a 16GB iPhone 3GS for £34 at CEX (Thrift Store) Mainly for music and taking pictures. I could go for the 32GB But there are none local to me, and I don't like ordering 2nd hand phones and tablets without seeing them in person first.

I'm thinking about jailbreaking the phone because I want to have a better experience. I know how to unbrick the phone if all fails, So I'm not worried about anything.

I know it does not go past iOS 6.1 Which is fine because I never really liked iOS 7
Opinions, please? If I ever get bored of it I could always sell it on ebay for alot more than what I paid for it…

I'll be getting a 12 month warranty aswell.
Does the USA have CEX Stores?

What happens if i black list my iphone while someone is using it?

I lost my iphone a fw days ago they swapped the sim because its still on find my iphone but they didn't take off my icloud. I honestly for got my password, so what will happen if i just black list the phone through att will it like immediately stop working or will they still be able to use it cause thy swapped sims?

My IPhone 6 was locked for security reasons? - 1

So I was using my iPhone 6 and I was on Facebook. I then decided to click on a video on Facebook, then it asked me to click ok to continue to watch the video. Then a pop up popped up on my phone saying "your apple device has been locked due to security reasons". I tried clicking ok so it could go away, but it didn't. I then clicked the home button, and turned my phone off for a little. When I turned it back on, I checked Facebook and the pop up was no longer there. Why did this happen? Is it something I should be concerned about?