diff --git a/src/mesh/NodeDB.cpp b/src/mesh/NodeDB.cpp
index f473027411..51b40445c0 100644
--- a/src/mesh/NodeDB.cpp
+++ b/src/mesh/NodeDB.cpp
@@ -1497,6 +1497,15 @@ void NodeDB::installDefaultModuleConfig()
 
     moduleConfig.has_canned_message = true;
 
+#ifdef SEEED_M2100
+    // Single-purpose data logger: poll the RS485 sensor without any client setup.
+    moduleConfig.serial.enabled = true;
+    moduleConfig.serial.mode = meshtastic_ModuleConfig_SerialConfig_Serial_Mode_MODBUS;
+    moduleConfig.serial.baud = meshtastic_ModuleConfig_SerialConfig_Serial_Baud_BAUD_9600;
+    moduleConfig.serial.rxd = PIN_SERIAL2_RX;
+    moduleConfig.serial.txd = PIN_SERIAL2_TX;
+#endif
+
 #if USERPREFS_MQTT_ENABLED && !MESHTASTIC_EXCLUDE_MQTT
     moduleConfig.mqtt.enabled = true;
 #endif
diff --git a/variants/stm32/seeed_m2100/platformio.ini b/variants/stm32/seeed_m2100/platformio.ini
new file mode 100644
index 0000000000..34f9d79723
--- /dev/null
+++ b/variants/stm32/seeed_m2100/platformio.ini
@@ -0,0 +1,23 @@
+; Seeed SenseCAP S2100 data logger, Meshtastic edition: RS485 Modbus sensor -> telemetry
+[env:seeed-m2100]
+extends = stm32_base
+board = lora_e5_dev_board
+board_level = extra
+board_upload.maximum_size = 247808 ; reserve the last 14KB for filesystem (reduced from 20KB in LittleFS.cpp)
+build_flags =
+  ${stm32_base.build_flags}
+  -Ivariants/stm32/seeed_m2100
+  -DPRIVATE_HW
+  -DSERIAL_UART_INSTANCE=1
+  -DPIN_SERIAL_RX=PB7
+  -DPIN_SERIAL_TX=PB6
+  ; TODO(S2100 schematic): RS485 UART pins are Wio-E5 dev board placeholders
+  -DENABLE_HWSERIAL2
+  -DPIN_SERIAL2_TX=PA2
+  -DPIN_SERIAL2_RX=PA3
+  -DMESHTASTIC_EXCLUDE_GPS=1
+  -DMESHTASTIC_EXCLUDE_I2C=1
+  -DMESHTASTIC_EXCLUDE_ENVIRONMENTAL_SENSOR=1
+  -DMESHTASTIC_EXCLUDE_AIR_QUALITY_SENSOR=1
+
+upload_port = stlink
diff --git a/variants/stm32/seeed_m2100/rfswitch.h b/variants/stm32/seeed_m2100/rfswitch.h
new file mode 100644
index 0000000000..3eadd9b5ca
--- /dev/null
+++ b/variants/stm32/seeed_m2100/rfswitch.h
@@ -0,0 +1,8 @@
+/* https://wiki.seeedstudio.com/LoRa-E5_STM32WLE5JC_Module/
+ * Wio-E5 module ONLY transmits through RFO_HP
+ * Receive: PA4=1, PA5=0
+ * Transmit(high output power, SMPS mode): PA4=0, PA5=1 */
+static const RADIOLIB_PIN_TYPE rfswitch_pins[5] = {PA4, PA5, RADIOLIB_NC, RADIOLIB_NC, RADIOLIB_NC};
+
+static const Module::RfSwitchMode_t rfswitch_table[4] = {
+    {STM32WLx::MODE_IDLE, {LOW, LOW}}, {STM32WLx::MODE_RX, {HIGH, LOW}}, {STM32WLx::MODE_TX_HP, {LOW, HIGH}}, END_OF_MODE_TABLE};
diff --git a/variants/stm32/seeed_m2100/variant.h b/variants/stm32/seeed_m2100/variant.h
new file mode 100644
index 0000000000..ba6d711614
--- /dev/null
+++ b/variants/stm32/seeed_m2100/variant.h
@@ -0,0 +1,29 @@
+/*
+Seeed SenseCAP S2100 data logger (Wio-E5 module, STM32WLE5JC) running Meshtastic.
+Polls an RS485 Modbus sensor and sends its readings as telemetry.
+*/
+
+#ifndef _VARIANT_SEEED_M2100_
+#define _VARIANT_SEEED_M2100_
+
+#define USE_STM32WLx
+
+#define SEEED_M2100
+
+// TODO(S2100 schematic): placeholders taken from the Wio-E5 dev board, not verified for the S2100.
+// The RS485 UART (Serial2, PIN_SERIAL2_TX PA2 -> transceiver DI, PIN_SERIAL2_RX PA3 <- RO) is set in
+// platformio.ini: the STM32 core instantiates Serial2 from build flags and never sees this file.
+// #define MODBUS_DE_PIN        <pin> // driver enable, if the transceiver is not auto-direction
+// #define MODBUS_PWR_EN_PIN    <pin> // switch for the 12 V sensor supply
+// #define MODBUS_PWR_WARMUP_MS 2000
+// #define BUTTON_PIN           <pin>
+// #define LED_POWER            <pin>
+
+// Client API tunnel on the RS485 bus, for provisioning without Bluetooth
+#define MODBUS_API_ADDR 240
+
+// LoRa
+// https://github.com/Seeed-Studio/LoRaWan-E5-Node/blob/163c05379b1805dd8f2c061d4557a69985acc953/Middlewares/Third_Party/SubGHz_Phy/stm32_radio_driver/radio_driver.c#L94
+#define SX126X_DIO3_TCXO_VOLTAGE 1.7
+
+#endif