diff --git a/owlps-positioning/src/stock.hh b/owlps-positioning/src/stock.hh
index db58fd3..ed540b5 100644
--- a/owlps-positioning/src/stock.hh
+++ b/owlps-positioning/src/stock.hh
@@ -68,6 +68,8 @@ public:
 
   /** @name Mobile operations */
   //@{
+  /// Returns the number of mobiles
+  static unsigned int nb_mobiles(void) ;
   /// Reads the Mobile corresponding to a given MAC address
   static const Mobile& get_mobile(const std::string &mac) ;
   /// \brief Searches for a Mobile given its MAC address and creates
@@ -178,6 +180,12 @@ find_create_waypoint(const Waypoint &point)
 /* *** Mobile operations *** */
 
 
+inline unsigned int Stock::nb_mobiles()
+{
+  return mobiles.size() ;
+}
+
+
 /**
  * If the Mobile corresponding to \em mac does not exist, it is created.
  * @param mac The MAC address of the Mobile to search for. It must be a