diff --git a/roc.py b/roc.py
index fe328aa..be609bf 100644
--- a/roc.py
+++ b/roc.py
@@ -9,6 +9,7 @@
 from requests.structures import CaseInsensitiveDict
 import logging as log
 import pyaml
+from datetime import datetime
 
 from device import Device
 
@@ -120,10 +121,17 @@
         return devices
 
     def update_devices(self, devices):
+        new = {}
         dgs = self.get_devicegroups()
         for dg in dgs:
             for d in dg['imsis']:
-                devices[str(d['imsi-range-from'])] = Device(str(d['imsi-id']), d['imsi-range-from'])
+                imsi_id = str(d['imsi-id'])
+                imsi = str(d['imsi-range-from'])
+                last_reachable = datetime.min
+                if imsi_id in devices:
+                    last_reachable = devices[imsi_id].last_reachable
+                new[imsi_id] = Device(imsi_id, imsi, last_reachable)
+        return new
 
     def get_subnet(self):
         subnets = {}