diff --git a/repeater/sensors/shtc3.py b/repeater/sensors/shtc3.py
new file mode 100644
index 0000000..7ec3099
--- /dev/null
+++ b/repeater/sensors/shtc3.py
@@ -0,0 +1,110 @@
+"""
+SHTC3 temperature and humidity sensor plug-in (RAK1901 WisBlock sensor).
+
+Requires: pip install smbus2
+
+The SHTC3 uses 16-bit command words and requires a raw I2C read (no register
+byte prefix), so smbus2.i2c_rdwr is used instead of the standard SMBus API.
+
+Config example:
+  - type: shtc3
+    name: "ambient"
+    enabled: true
+    auto_install_packages: false
+    settings:
+      i2c_address: 0x70  # SHTC3 fixed I2C address
+      bus_number: 1       # I2C bus number (1 for Raspberry Pi default)
+"""
+
+from __future__ import annotations
+
+import time
+from typing import Any, Dict, Optional
+
+from .base import SensorBase
+from .registry import SensorRegistry
+
+# SHTC3 two-byte command words
+_CMD_WAKE  = [0x35, 0x17]
+_CMD_MEAS  = [0x7C, 0xA2]  # T-first, normal power mode
+_CMD_SLEEP = [0xB0, 0x98]
+
+
+@SensorRegistry.register("shtc3")
+class SHTC3Sensor(SensorBase):
+    sensor_type = "shtc3"
+
+    def __init__(self, name: str, config: Optional[Dict[str, Any]] = None, log=None):
+        super().__init__(name=name, config=config, log=log)
+
+        self.i2c_address = int(self.settings.get("i2c_address", 0x70))
+        self.bus_number = int(self.settings.get("bus_number", 1))
+
+        self.available = False
+
+        if not self.ensure_python_modules([("smbus2", "smbus2")]):
+            return
+
+        try:
+            import smbus2  # type: ignore[import-not-found]
+            self._smbus2 = smbus2
+
+            # Verify sensor is reachable: wake then immediately sleep
+            bus = smbus2.SMBus(self.bus_number)
+            try:
+                bus.i2c_rdwr(smbus2.i2c_msg.write(self.i2c_address, _CMD_WAKE))
+                time.sleep(0.002)
+                bus.i2c_rdwr(smbus2.i2c_msg.write(self.i2c_address, _CMD_SLEEP))
+            finally:
+                bus.close()
+
+            self.available = True
+            self.log.info(
+                "SHTC3 initialized (addr=0x%02X, bus=%d)",
+                self.i2c_address,
+                self.bus_number,
+            )
+        except Exception as exc:
+            self.log.warning(
+                "SHTC3 init failed (addr=0x%02X, bus=%d): %s",
+                self.i2c_address,
+                self.bus_number,
+                exc,
+            )
+            self.available = False
+
+    def _read(self) -> Dict[str, Any]:
+        """Read temperature and humidity from SHTC3."""
+        if not self.available:
+            raise RuntimeError("SHTC3 device not available")
+
+        smbus2 = self._smbus2
+        bus = smbus2.SMBus(self.bus_number)
+        try:
+            bus.i2c_rdwr(smbus2.i2c_msg.write(self.i2c_address, _CMD_WAKE))
+            time.sleep(0.002)
+            bus.i2c_rdwr(smbus2.i2c_msg.write(self.i2c_address, _CMD_MEAS))
+            time.sleep(0.02)  # measurement takes ~12 ms in normal power mode
+
+            r = smbus2.i2c_msg.read(self.i2c_address, 6)
+            bus.i2c_rdwr(r)
+            data = list(r)
+
+            bus.i2c_rdwr(smbus2.i2c_msg.write(self.i2c_address, _CMD_SLEEP))
+
+            # Bytes: T_MSB, T_LSB, T_CRC, RH_MSB, RH_LSB, RH_CRC
+            t_raw  = (data[0] << 8) | data[1]
+            rh_raw = (data[3] << 8) | data[4]
+            temp_c = round(-45.0 + 175.0 * t_raw / 65536.0, 2)
+            temp_f = round(temp_c * 9.0 / 5.0 + 32.0, 2)
+            rh     = round(100.0 * rh_raw / 65536.0, 2)
+
+            return {
+                "temperature_c": temp_c,
+                "temperature_f": temp_f,
+                "humidity_pct":  rh,
+            }
+        except Exception as exc:
+            raise RuntimeError(f"SHTC3 read failed: {exc}") from exc
+        finally:
+            bus.close()
diff --git a/repeater/sensors/waveshare_ups_d.py b/repeater/sensors/waveshare_ups_d.py
new file mode 100644
index 0000000..5b62232
--- /dev/null
+++ b/repeater/sensors/waveshare_ups_d.py
@@ -0,0 +1,148 @@
+"""
+Waveshare UPS HAT (D) battery monitor plug-in — INA219 at I2C 0x43.
+
+Reads a single 21700 Li-ion cell via INA219. Reports voltage, current,
+power, battery percent, and charge state.
+
+Requires: pip install smbus2
+
+Config example:
+  - type: waveshare_ups_d
+    name: "battery"
+    enabled: true
+    auto_install_packages: false
+    settings:
+      i2c_address: 0x43  # Waveshare UPS HAT (D) fixed address
+      bus_number: 1       # I2C bus number (1 for Raspberry Pi default)
+"""
+
+from __future__ import annotations
+
+import time
+from typing import Any, Dict, Optional
+
+from .base import SensorBase
+from .registry import SensorRegistry
+
+# INA219 register addresses
+_REG_CONFIG = 0x00
+_REG_SHUNT  = 0x01
+_REG_BUS    = 0x02
+_REG_POWER  = 0x03
+_REG_CURRENT = 0x04
+_REG_CAL    = 0x05
+
+# 32V range, ±320mV gain, 128-sample averaging, continuous shunt+bus
+_CONFIG_VALUE = 0x3FFF
+
+# Waveshare UPS HAT (D) calibration — 0.01Ω shunt (per Waveshare sample code)
+# current_lsb ≈ 0.1524 mA/LSB, power_lsb = current_lsb × 20
+_CAL_VALUE   = 26868
+_CURRENT_LSB = 0.0001524   # A per LSB
+_POWER_LSB   = _CURRENT_LSB * 20.0  # W per LSB
+
+
+def _voltage_to_percent(v: float) -> int:
+    """Piecewise linear SoC estimate for a single 21700 Li-ion cell (3.0–4.2 V)."""
+    if v >= 4.20: return 100
+    if v >= 4.00: return int(85 + (v - 4.00) / 0.20 * 15)
+    if v >= 3.80: return int(60 + (v - 3.80) / 0.20 * 25)
+    if v >= 3.70: return int(40 + (v - 3.70) / 0.10 * 20)
+    if v >= 3.50: return int(15 + (v - 3.50) / 0.20 * 25)
+    if v >= 3.00: return int(       (v - 3.00) / 0.50 * 15)
+    return 0
+
+
+@SensorRegistry.register("waveshare_ups_d")
+class WaveshareUpsDSensor(SensorBase):
+    sensor_type = "waveshare_ups_d"
+
+    def __init__(self, name: str, config: Optional[Dict[str, Any]] = None, log=None):
+        super().__init__(name=name, config=config, log=log)
+
+        self.i2c_address = int(self.settings.get("i2c_address", 0x43))
+        self.bus_number  = int(self.settings.get("bus_number", 1))
+
+        self.available = False
+
+        if not self.ensure_python_modules([("smbus2", "smbus2")]):
+            return
+
+        try:
+            import smbus2  # type: ignore[import-not-found]
+            self._smbus2 = smbus2
+
+            bus = smbus2.SMBus(self.bus_number)
+            try:
+                self._write(bus, _REG_CONFIG, _CONFIG_VALUE)
+                self._write(bus, _REG_CAL, _CAL_VALUE)
+                # 128-sample averaging takes ~68 ms; wait for first conversion
+                time.sleep(0.15)
+            finally:
+                bus.close()
+
+            self.available = True
+            self.log.info(
+                "Waveshare UPS HAT (D) INA219 initialized (addr=0x%02X, bus=%d)",
+                self.i2c_address,
+                self.bus_number,
+            )
+        except Exception as exc:
+            self.log.warning(
+                "Waveshare UPS HAT (D) init failed (addr=0x%02X, bus=%d): %s",
+                self.i2c_address,
+                self.bus_number,
+                exc,
+            )
+
+    def _write(self, bus, reg: int, val: int) -> None:
+        bus.write_i2c_block_data(
+            self.i2c_address, reg, [(val >> 8) & 0xFF, val & 0xFF]
+        )
+
+    def _read_u(self, bus, reg: int) -> int:
+        d = bus.read_i2c_block_data(self.i2c_address, reg, 2)
+        return (d[0] << 8) | d[1]
+
+    def _read_s(self, bus, reg: int) -> int:
+        v = self._read_u(bus, reg)
+        return v - 0x10000 if v & 0x8000 else v
+
+    def _read(self) -> Dict[str, Any]:
+        """Read voltage, current, power, and derived battery state."""
+        if not self.available:
+            raise RuntimeError("Waveshare UPS HAT (D) not available")
+
+        try:
+            bus = self._smbus2.SMBus(self.bus_number)
+            try:
+                # Re-apply calibration in case of external reset
+                self._write(bus, _REG_CAL, _CAL_VALUE)
+
+                bus_v     = (self._read_u(bus, _REG_BUS) >> 3) * 4 / 1000.0
+                shunt_mv  = self._read_s(bus, _REG_SHUNT) * 0.01
+                current_ma = self._read_s(bus, _REG_CURRENT) * _CURRENT_LSB * 1000.0
+                power_mw  = self._read_u(bus, _REG_POWER) * _POWER_LSB * 1000.0
+            finally:
+                bus.close()
+
+            pct = _voltage_to_percent(bus_v)
+
+            # HAT (D) sign convention: negative = charging, positive = discharging
+            if current_ma < -50:
+                state = "charging"
+            elif current_ma > 50:
+                state = "discharging"
+            else:
+                state = "idle"
+
+            return {
+                "bus_voltage_v":    round(bus_v, 3),
+                "shunt_voltage_mv": round(shunt_mv, 2),
+                "current_ma":       round(current_ma, 1),
+                "power_mw":         round(power_mw, 1),
+                "battery_percent":  pct,
+                "charge_state":     state,
+            }
+        except Exception as exc:
+            raise RuntimeError(f"Waveshare UPS HAT (D) read failed: {exc}") from exc