expressjs, mongoose, Schema error

So. I'm attempting to use mongoDB with an expressjs project using mongoose, and I get this error.

throw new mongoose.Error.MissingSchemaError(name);
        ^
MissingSchemaError: Schema hasn't been registered for model "device".

I am also new here but here is my source code for index.js where I am getting the error for var device

var mongoose = require('mongoose');
var device = mongoose.model('device', device);

/* GET */
router.get('/', function(req, res) {
    new device({
        device_id    : "Something happened"
      }).save( function( err, device, count ){
        res.redirect( '/' );
    });     
});

here is the code I have in app.js:

//mongo start
var mongo = require('mongodb');
var mongoose = require('mongoose');
var Schema = mongoose.Schema;

var device = new Schema({
    device_id : String
});

var device = mongoose.model('device', device);

var db = mongoose.connect('mongodb://127.0.0.1:27017/database');

mongoose.connection.once('connected', function() {
    console.log("Connected to database")
});
//mongo end