@Path("devices/{deviceLibraryIdentifier}/registrations/{passTypeIdentifier}")
 @GET
 public Response getSerialNumbersOfPassesAssociatedWithDevice(
     @PathParam("deviceLibraryIdentifier") String deviceLibraryIdentifier,
     @PathParam("passTypeIdentifier") String passTypeIdentifier,
     @QueryParam("passesUpdatedSince") @DefaultValue("") String passesUpdatedSince) {
   DeviceDAO device = new DeviceDAO(deviceLibraryIdentifier);
   ListOfPasses passes = new ListOfPasses();
   passes.setLastUpdated(DateUtil.getTimeStamp());
   if (device.retrieve()) {
     for (Registration reg : device.getRegistrations()) {
       if (passTypeIdentifier.equals(reg.getPassTypeIdentifier())) {
         passes.addSerialNumber(reg.getSerialNumber());
       }
     }
   }
   if (passes.getSerialNumbers().size() > 0) {
     return Response.status(Response.Status.OK).entity(passes.toJson(Pass.PRETTY)).build();
   }
   return Response.status(Response.Status.NO_CONTENT).build();
 }