diff --git a/reactor-plc/plc.lua b/reactor-plc/plc.lua
index 6f9622d..f0f00b1 100644
--- a/reactor-plc/plc.lua
+++ b/reactor-plc/plc.lua
@@ -282,7 +282,7 @@ function comms_init(id, modem, local_port, server_port, reactor, iss)
 
     -- keep alive ack
     local _send_keep_alive_ack = function (srv_time)
-        _send(RPLC_TYPES.KEEP_ALIVE, { srv_time, os.time() })
+        _send(RPLC_TYPES.KEEP_ALIVE, { srv_time, os.epoch() })
     end
 
     -- general ack
@@ -368,7 +368,7 @@ function comms_init(id, modem, local_port, server_port, reactor, iss)
                     if packet.type == RPLC_TYPES.KEEP_ALIVE then
                         -- keep alive request received, echo back
                         local timestamp = packet.data[1]
-                        local trip_time = os.time() - timestamp
+                        local trip_time = os.epoch() - timestamp
 
                         if trip_time < 0 then
                             log._warning("PLC KEEP_ALIVE trip time less than 0 (" .. trip_time .. ")") 
@@ -490,7 +490,7 @@ function comms_init(id, modem, local_port, server_port, reactor, iss)
         end
 
         local sys_status = {
-            os.time(),
+            os.epoch(),
             (not self.scrammed),
             overridden,
             degraded,
diff --git a/scada-common/alarm.lua b/scada-common/alarm.lua
index b93df73..d6670a4 100644
--- a/scada-common/alarm.lua
+++ b/scada-common/alarm.lua
@@ -9,7 +9,7 @@ SEVERITY = {
 
 function scada_alarm(severity, device, message)
     local self = {
-        time = os.time(),
+        time = os.epoch(),
         ts_string = os.date("[%H:%M:%S]"),
         severity = severity,
         device = device,