SCSS / Sass mixin for responsive sites

responsive mixin

$small-desktop: 960px;
$large-desktop: 1200px;
$handheld: 768px;
$handhelds-landscape: 1024px;
$mobile: 640px;
$mobile-landscape: 480px;

@mixin respond-to($media) {
  @if $media == largeDesktop {
    @media only screen and (min-width: $large-desktop) { @content }
  }
  @if $media == smallDesktop {
    @media only screen and (max-width: $small-desktop) { @content; }
  }
  @if $media == handhelds {
    @media only screen and (max-width: $handheld) { @content; }
  }
  @if $media == handhelds-landscape {
    @media only screen  and (min-device-width : $handheld)
                        and (max-device-width : $handhelds-landscape)
                        and (orientation : landscape){ @content; }
  }
  @if $media == mobile {
    @media only screen and (max-width: $mobile) { @content; }
  }
  @if $media == mobile-portrait {
    @media only screen  and (max-width: $mobile)
                        and (orientation : portrait) { @content; }
  }
  @if $media == mobile-landscape {
    @media only screen  and (min-width: 320px)
                        and (max-width: $mobile-landscape)
                        and (orientation : landscape) { @content; }
  }

  @if $media == retina {
    @media (-webkit-min-device-pixel-ratio: 2) { @content; }
  }

  @if $media == iphone5 {
    @media only screen and (device-aspect-ratio: 40/71) { @content }
  }
}

/* To be used like this */

body {
  @include respond-to(handhelds){
    // css code here
  }
}

Didn't you mix up the resolutions for mobile and mobile landscape? :)