MySQLi使用另一个准备好的语句中的参数准备语句

I'm trying to switch to prepared statements because of the SQL-injection protection that they offer, but I am currently stuck with this.

How do you make a prepared statement query, using data from another one as params?

What I mean is this: If i have a table with people, and another one with their devices, and I want to list all people with all their devices. How do I do that?

What I want to achive is something like this:

    Alex: Pc, Laptop, Mobile
    Annie: Laptop, Mobile
    Danny: Mobile, Printer

What I have written so far is this:

    $people_query = "SELECT id, name FROM people";
    $device_query = "SELECT device_name FROM devices WHERE owner_id = ?";

    if(!$pplstmt = $mysqli -> prepare($people_query)) die("Couldn't prepare people statement!");
    if(!$devstmt = $mysqli -> prepare($device_query)) die("Couldn't prepare device statement!");

    $pplstmt -> execute();
    $pplstmt -> bind_result($person_id, $person_name);
    while($pplstmt->fetch()){

            echo $person_name . ':';

            $devstmt -> bind_param("i", $person_id);    
            $devstmt -> execute();
            $devstmt -> bind_result($device_name);
            while($devstmt->fetch()){
                echo $device_name . ',';
            }
      }
      $pplstmt -> close();
      $devstmt -> close();

I have moved the prepare statement of the second query out of the loop, because I read that this way it won't initialize again, and again, and again...

This however doesn't work. Any ideas, or advices?