user41218: I would like you to give me some clues about a projet I have: I want to make sure that my little brother's smartphone stays in a shelf overnight and during school hours in order to monitor the time he spends with it.
In order to fulfill my needs, I thought of using an Arduino to detect that the smartphone stays in proximity at certain hours.
Since this is my first Arduino project, I'm not quite sure what I could do, and what is possible to do.
Hence I've got a lot of questions:

Can I easily detect that a specific smartphone is in range?
Can I use the smartphone's NFC (RFID) to do so?
What kind of output could I possibly get from an Arduino? I would like to make statistics, so it must be stored somewhere, and I know Arduino doesn't have a lot of memory.
Is it possible to write on a USB key?
Which Arduino is best suited for my needs Should I consider buying an Arduino with Ethernet in order to send emails?

Thanks a lot!

user4143: 
Can I easily detect that a specific smartphone is in proximity ?

It can be done, yes. How "easily" depends on how much money and expertise you have to throw at it.

Can I use the smartphone's NFC (RFID) to do so ?

It is possible to use that, yes - if you add the right hardware and software to the Arduino.

How long can an Arduino run on battery using a 9V battery from the market ?

A couple of hours if you're lucky. They are useless batteries.

What kind of output could I possibly get from an Arduino ? I would like to make statistics, so it must be stored somewhere, and I know Arduino has not a lot of memory.

Whatever you want. Again, it's SMOP / SMOH.

Is it possible to write on an USB key ?

Sure, if you get the right hardware for that.

Which Arduino is best suited for my needs ? Should I consider buying an Arduino with Ethernet in order so send email ?

The Arduino that provides the facilities your project requires - and that depends on how you are going to decide on how to do it. Remember: the Arduino is just the "brain" of the operation. You need to decide what "organs" the brain needs to control and in what way. 
There's a million and one ways of achieving what you want. You could even do it 100% in the phone in software (there's probably an app for that...) without need of an Arduino...

41218: <p>I would like you to give me some clues about a projet I have: I want to make sure that my little brother's smartphone stays in a shelf overnight and during school hours in order to monitor the time he spends with it.</p>

<p>In order to fulfill my needs, I thought of using an Arduino to detect that the smartphone stays in proximity at certain hours.</p>

<p>Since this is my first Arduino project, I'm not quite sure what I could do, and what is possible to do.</p>

<p>Hence I've got a lot of questions:</p>

<ul>
<li>Can I easily detect that a specific smartphone is in range?</li>
<li>Can I use the smartphone's NFC (RFID) to do so?</li>
<li>What kind of output could I possibly get from an Arduino? I would like to make statistics, so it must be stored somewhere, and I know Arduino doesn't have a lot of memory.</li>
<li>Is it possible to write on a USB key?</li>
<li>Which Arduino is best suited for my needs Should I consider buying an Arduino with Ethernet in order to send emails?</li>
</ul>

<p>Thanks a lot!</p>
 4143: <blockquote>
  <p>Can I easily detect that a specific smartphone is in proximity ?</p>
</blockquote>

<p>It can be done, yes. How "easily" depends on how much money and expertise you have to throw at it.</p>

<blockquote>
  <p>Can I use the smartphone's NFC (RFID) to do so ?</p>
</blockquote>

<p>It is possible to use that, yes - if you add the right hardware and software to the Arduino.</p>

<blockquote>
  <p>How long can an Arduino run on battery using a 9V battery from the market ?</p>
</blockquote>

<p>A couple of hours if you're lucky. They are useless batteries.</p>

<blockquote>
  <p>What kind of output could I possibly get from an Arduino ? I would like to make statistics, so it must be stored somewhere, and I know Arduino has not a lot of memory.</p>
</blockquote>

<p>Whatever you want. Again, it's SMOP / SMOH.</p>

<blockquote>
  <p>Is it possible to write on an USB key ?</p>
</blockquote>

<p>Sure, if you get the right hardware for that.</p>

<blockquote>
  <p>Which Arduino is best suited for my needs ? Should I consider buying an Arduino with Ethernet in order so send email ?</p>
</blockquote>

<p>The Arduino that provides the facilities your project requires - and that depends on how you are going to decide on how to do it. Remember: the Arduino is just the "brain" of the operation. You need to decide what "organs" the brain needs to control and in what way. </p>

<p>There's a million and one ways of achieving what you want. You could even do it 100% in the phone in software (there's probably an app for that...) without need of an Arduino...</p>
