diff --git a/Conf.cpp b/Conf.cpp
index 0c04165..87eb796 100644
--- a/Conf.cpp
+++ b/Conf.cpp
@@ -55,7 +55,8 @@ enum SECTION {
   SECTION_NEXTION,
   SECTION_OLED,
   SECTION_LCDPROC,
-  SECTION_TGREWRITE
+  SECTION_TGREWRITE,
+  SECTION_LOCKFILE
 };
 
 CConf::CConf(const std::string& file) :
@@ -238,7 +239,9 @@ m_lcdprocAddress(),
 m_lcdprocPort(0U),
 m_lcdprocLocalPort(0U),
 m_lcdprocDisplayClock(false),
-m_lcdprocUTC(false)
+m_lcdprocUTC(false),
+m_lockFileEnabled(false),
+m_lockFileName()
 {
 }
 
@@ -314,6 +317,8 @@ bool CConf::read()
 		  section = SECTION_OLED;
 	  else if (::strncmp(buffer, "[LCDproc]", 9U) == 0)
 		  section = SECTION_LCDPROC;
+	  else if (::strncmp(buffer, "[LOCKFILE]", 9U) == 0)
+		  section = SECTION_LOCKFILE;
 	  else
 		  section = SECTION_NONE;
 
@@ -785,6 +790,11 @@ bool CConf::read()
 			m_lcdprocUTC = ::atoi(value) == 1;
 		else if (::strcmp(key, "DimOnIdle") == 0)
 			m_lcdprocDimOnIdle = ::atoi(value) == 1;
+	} else if (section == SECTION_LOCKFILE) {
+		if (::strcmp(key, "Enable") == 0)
+			m_lockFileEnabled = ::atoi(value) == 1;
+		else if (::strcmp(key, "File") == 0)
+			m_lockFileName = value;
 	}
   }
 
@@ -1692,3 +1702,13 @@ bool CConf::getNextionTempInFahrenheit() const
 {
 	return m_nextionTempInFahrenheit;
 }
+
+bool CConf::getLockFileEnabled() const
+{
+	return m_lockFileEnabled;
+}
+
+std::string CConf::getLockFileName() const
+{
+	return m_lockFileName;
+}
diff --git a/Conf.h b/Conf.h
index efff32b..f9f0de3 100644
--- a/Conf.h
+++ b/Conf.h
@@ -262,6 +262,11 @@ public:
   bool         getLCDprocUTC() const;
   bool         getLCDprocDimOnIdle() const;
 
+  // The Lock File section
+  bool         getLockFileEnabled() const;
+  std::string  getLockFileName() const;
+
+
 private:
   std::string  m_file;
   std::string  m_callsign;
@@ -469,6 +474,9 @@ private:
   bool         m_lcdprocDisplayClock;
   bool         m_lcdprocUTC;
   bool         m_lcdprocDimOnIdle;
+
+  bool         m_lockFileEnabled;
+  std::string  m_lockFileName;
 };
 
 #endif
diff --git a/DMRSlot.cpp b/DMRSlot.cpp
index b8715e0..65c6dd8 100644
--- a/DMRSlot.cpp
+++ b/DMRSlot.cpp
@@ -826,6 +826,8 @@ bool CDMRSlot::writeModem(unsigned char *data, unsigned int len)
 					return false;
 				if (m_rfN == m_lastrfN)
 					return false;
+				if (m_rfN != (m_lastrfN + 1U))
+					return false;
 				m_lastrfN = m_rfN;
 
 				// Regenerate the EMB
diff --git a/MMDVM.ini b/MMDVM.ini
index 7e94c0e..d654a61 100644
--- a/MMDVM.ini
+++ b/MMDVM.ini
@@ -240,3 +240,7 @@ Port=13666
 DimOnIdle=0
 DisplayClock=1
 UTC=0
+
+[LOCKFILE]
+Enable=0
+File=/tmp/MMDVM_Active.lck
diff --git a/MMDVMHost.cpp b/MMDVMHost.cpp
index 52e8025..ff0bb42 100644
--- a/MMDVMHost.cpp
+++ b/MMDVMHost.cpp
@@ -155,7 +155,9 @@ m_dmrLookup(NULL),
 m_nxdnLookup(NULL),
 m_callsign(),
 m_id(0U),
-m_cwCallsign()
+m_cwCallsign(),
+m_lockFileEnabled(false),
+m_lockFileName()
 {
 }
 
@@ -342,6 +344,12 @@ int CMMDVMHost::run()
 		m_modem->setTransparentDataParams(sendFrameType);
 	}
 
+	if (m_conf.getLockFileEnabled()) {
+		m_lockFileName = m_conf.getLockFileName();
+		LogInfo("Lock File Parameters");
+		LogInfo("    Name: %s", m_lockFileName.c_str());
+	}
+
 	if (m_conf.getCWIdEnabled()) {
 		unsigned int time = m_conf.getCWIdTime();
 		m_cwCallsign      = m_conf.getCWIdCallsign();
@@ -576,6 +584,7 @@ int CMMDVMHost::run()
 	while (!m_killed) {
 		bool lockout1 = m_modem->hasLockout();
 		bool lockout2 = false;
+
 		if (m_ump != NULL)
 			lockout2 = m_ump->getLockout();
 		if ((lockout1 || lockout2) && m_mode != MODE_LOCKOUT)
@@ -596,6 +605,9 @@ int CMMDVMHost::run()
 			m_ump->setCD(cd);
 		}
 
+		if (m_mode == MODE_IDLE)
+			removeLockFile();
+
 		unsigned char data[200U];
 		unsigned int len;
 		bool ret;
@@ -1381,6 +1393,7 @@ void CMMDVMHost::setMode(unsigned char mode)
 		m_mode = MODE_DSTAR;
 		m_modeTimer.start();
 		m_cwIdTimer.stop();
+		createLockFile();
 		break;
 
 	case MODE_DMR:
@@ -1404,6 +1417,7 @@ void CMMDVMHost::setMode(unsigned char mode)
 		m_mode = MODE_DMR;
 		m_modeTimer.start();
 		m_cwIdTimer.stop();
+		createLockFile();
 		break;
 
 	case MODE_YSF:
@@ -1423,6 +1437,7 @@ void CMMDVMHost::setMode(unsigned char mode)
 		m_mode = MODE_YSF;
 		m_modeTimer.start();
 		m_cwIdTimer.stop();
+		createLockFile();
 		break;
 
 	case MODE_P25:
@@ -1442,6 +1457,7 @@ void CMMDVMHost::setMode(unsigned char mode)
 		m_mode = MODE_P25;
 		m_modeTimer.start();
 		m_cwIdTimer.stop();
+		createLockFile();
 		break;
 
 	case MODE_NXDN:
@@ -1461,6 +1477,7 @@ void CMMDVMHost::setMode(unsigned char mode)
 		m_mode = MODE_NXDN;
 		m_modeTimer.start();
 		m_cwIdTimer.stop();
+		createLockFile();
 		break;
 
 	case MODE_POCSAG:
@@ -1480,6 +1497,7 @@ void CMMDVMHost::setMode(unsigned char mode)
 		m_mode = MODE_POCSAG;
 		m_modeTimer.start();
 		m_cwIdTimer.stop();
+		createLockFile();
 		break;
 
 	case MODE_LOCKOUT:
@@ -1564,11 +1582,41 @@ void CMMDVMHost::setMode(unsigned char mode)
 			m_cwIdTimer.start();
 		}
 		m_display->setIdle();
-		if (mode==MODE_QUIT) {
+		if (mode == MODE_QUIT) {
 			m_display->setQuit();
+			removeLockFile();
 		}
 		m_mode = MODE_IDLE;
 		m_modeTimer.stop();
+		removeLockFile();
 		break;
 	}
 }
+
+void  CMMDVMHost::createLockFile()
+{
+	if (m_lockFileEnabled) {
+		FILE* fp = ::fopen(m_lockFileName.c_str(), "r");
+		if (fp == NULL) { //if file does not exist, create it
+			fp = ::fopen(m_lockFileName.c_str(), "wt");
+			if (fp != NULL) {
+				::fputs("ACTIVE\n", fp);
+				::fclose(fp);
+			}
+		}
+		else {
+			::fclose(fp);
+		}
+	}
+}
+
+void  CMMDVMHost::removeLockFile()
+{
+	if (m_lockFileEnabled) {
+		FILE* fp = ::fopen(m_lockFileName.c_str(), "r");
+		if (fp != NULL) {
+			::fclose(fp);
+			::remove(m_lockFileName.c_str());
+		}
+	}
+}
diff --git a/MMDVMHost.h b/MMDVMHost.h
index 889fe69..645437c 100644
--- a/MMDVMHost.h
+++ b/MMDVMHost.h
@@ -35,6 +35,8 @@
 
 #include <string>
 
+
+
 class CMMDVMHost
 {
 public:
@@ -83,6 +85,8 @@ private:
   std::string     m_callsign;
   unsigned int    m_id;
   std::string     m_cwCallsign;
+  bool            m_lockFileEnabled;
+  std::string     m_lockFileName;
 
   void readParams();
   bool createModem();
@@ -94,6 +98,9 @@ private:
   bool createPOCSAGNetwork();
 
   void setMode(unsigned char mode);
+
+  void createLockFile();
+  void removeLockFile();
 };
 
 #endif