diff --git a/succbone/succd/modbus.go b/succbone/succd/modbus.go
index ed33f7e..e5f3b91 100644
--- a/succbone/succd/modbus.go
+++ b/succbone/succd/modbus.go
@@ -40,28 +40,27 @@ func (d *daemon) modbusConnect() error {
 // The first one (slave 1) is a temperature/humidity sensor.
 // The second one (slave 2) is a PTA8D08 transmitter
 func (d *daemon) modbusUpdate() error {
-	d.mu.Lock()
-	defer d.mu.Unlock()
-
 	var err error
-	var registers []uint16 // temperature, humidity
 
-	// Switch to slave 1
+	// Switch to slave 1 (BTA1)
 	d.modbusClient.SetUnitId(1)
 
 	// Read temperature and humidity
-	registers, err = d.modbusClient.ReadRegisters(1, 2, modbus.INPUT_REGISTER)
+	var registersBTA1 []uint16 // temperature, humidity
+	registersBTA1, err = d.modbusClient.ReadRegisters(1, 2, modbus.INPUT_REGISTER)
 	if err != nil {
 		return err
 	}
 
-	if len(registers) != 2 {
-		msg := fmt.Sprintf("Expected two registers from modbus slave 1, but got %d", len(registers))
+	if len(registersBTA1) != 2 {
+		msg := fmt.Sprintf("Expected two registers from modbus slave 1, but got %d", len(registersBTA1))
 		return errors.New(msg)
 	}
 
-	d.daemonState.tempSEM = modbusValuesToFloat(registers[0])
-	d.daemonState.humiditySEM = modbusValuesToFloat(registers[1])
+	d.mu.Lock()
+	d.daemonState.tempSEM = modbusValuesToFloat(registersBTA1[0])
+	d.daemonState.humiditySEM = modbusValuesToFloat(registersBTA1[1])
+	d.mu.Unlock()
 
 	// Switch to slave 2 (KEC2)
 	d.modbusClient.SetUnitId(2)
@@ -70,18 +69,21 @@ func (d *daemon) modbusUpdate() error {
 	// Channel 0: Cable -WGA6, Sensor "dp bottom"
 	// Channel 1: Cable -WGA8, Sensor "dp inlet"
 	// Channel 2: Cable WGA7, Sensor "dp top"
-	registers, err = d.modbusClient.ReadRegisters(0, 3, modbus.HOLDING_REGISTER)
+	var registersKEC2 []uint16 // temperatures dp
+	registersKEC2, err = d.modbusClient.ReadRegisters(0, 3, modbus.HOLDING_REGISTER)
 	if err != nil {
 		return err
 	}
 
-	if len(registers) != 3 {
-		return fmt.Errorf("expected three registers from modbus slave 2, but got %d", len(registers))
+	if len(registersKEC2) != 3 {
+		return fmt.Errorf("expected three registers from modbus slave 2, but got %d", len(registersKEC2))
 	}
 
-	d.daemonState.tempDPBottom = modbusValuesToFloat(registers[0])
-	d.daemonState.tempDPInlet = modbusValuesToFloat(registers[1])
-	d.daemonState.tempDPTop = modbusValuesToFloat(registers[2])
+	d.mu.Lock()
+	d.daemonState.tempDPBottom = modbusValuesToFloat(registersKEC2[0])
+	d.daemonState.tempDPInlet = modbusValuesToFloat(registersKEC2[1])
+	d.daemonState.tempDPTop = modbusValuesToFloat(registersKEC2[2])
+	d.mu.Unlock()
 
 	// Switch to slave 3 (KEC1)
 	d.modbusClient.SetUnitId(3)
@@ -106,7 +108,7 @@ func (d *daemon) modbusUpdate() error {
 
 	// KFA1-KFA8
 	var relayState [8]bool
-
+	d.mu.Lock()
 	// -KFA1 Roughing Pump (normally closed contact)
 	relayState[0] = !d.daemonState.rpOn
 	// -KFA2 Diffusion Pump
@@ -119,23 +121,24 @@ func (d *daemon) modbusUpdate() error {
 	relayState[5] = !d.aboveRough.output
 	// -KFA7 Fake-Pirani High (normally closed contact)
 	relayState[6] = !d.aboveHigh.output
+	d.mu.Unlock()
 
 	// The KEC1 module uses a non-standard MODBUS interface
 	// instead of coils
 	// 0x0100 is the open command
 	// 0x0200 is the close command
 	// We write 8 words (16-bit) to address 0x01 to update the relays
-	var registerValues [8]uint16
+	var registerValuesKEC1 [8]uint16
 	// Convert the boolean values to the commands
 	for idx, state := range relayState {
 		if state {
-			registerValues[idx] = 0x0100
+			registerValuesKEC1[idx] = 0x0100
 		} else {
-			registerValues[idx] = 0x0200
+			registerValuesKEC1[idx] = 0x0200
 		}
 	}
 
-	err = d.modbusClient.WriteRegisters(0x01, registerValues[:])
+	err = d.modbusClient.WriteRegisters(0x01, registerValuesKEC1[:])
 	if err != nil {
 		return err
 	}