diff --git a/MAX_INTEGRATION.md b/MAX_INTEGRATION.md
new file mode 100644
index 0000000..63b4868
--- /dev/null
+++ b/MAX_INTEGRATION.md
@@ -0,0 +1,223 @@
+# MAX! (eQ-3) Thermostat Integration
+
+## Overview
+
+This document describes the integration of MAX! (eQ-3) thermostats via Homegear into the home automation system.
+
+## Protocol Characteristics
+
+MAX! thermostats use a **simple integer-based protocol** (not JSON):
+
+- **SET messages**: Plain integer temperature value (e.g., `22`)
+- **STATE messages**: Plain integer temperature value (e.g., `22`)
+- **Topics**: Homegear MQTT format
+
+### MQTT Topics
+
+**SET Command:**
+```
+homegear/instance1/set/<peerId>/<channel>/SET_TEMPERATURE
+Payload: "22" (plain integer as string)
+```
+
+**STATE Update:**
+```
+homegear/instance1/plain/<peerId>/<channel>/SET_TEMPERATURE
+Payload: "22" (plain integer as string)
+```
+
+## Transformation Layer
+
+The abstraction layer provides automatic transformation between the abstract home protocol and MAX! format.
+
+### Abstract → MAX! (SET)
+
+**Input (Abstract):**
+```json
+{
+  "mode": "heat",
+  "target": 22.5
+}
+```
+
+**Output (MAX!):**
+```
+22
+```
+
+**Transformation Rules:**
+- Extract `target` temperature
+- Convert float → integer (round to nearest)
+- Return as plain string (no JSON)
+- Ignore `mode` field (MAX! always in heating mode)
+
+### MAX! → Abstract (STATE)
+
+**Input (MAX!):**
+```
+22
+```
+
+**Output (Abstract):**
+```json
+{
+  "target": 22.0,
+  "mode": "heat"
+}
+```
+
+**Transformation Rules:**
+- Parse plain string/integer value
+- Convert to float
+- Add default `mode: "heat"` (MAX! always heating)
+- Wrap in abstract payload structure
+
+## Device Configuration
+
+### Example devices.yaml Entry
+
+```yaml
+- device_id: "thermostat_wolfgang"
+  type: "thermostat"
+  cap_version: "thermostat@1.0.0"
+  technology: "max"
+  features:
+    mode: true
+    target: true
+    current: false  # SET_TEMPERATURE doesn't report current temp
+  topics:
+    set: "homegear/instance1/set/39/1/SET_TEMPERATURE"
+    state: "homegear/instance1/plain/39/1/SET_TEMPERATURE"
+  metadata:
+    friendly_name: "Thermostat Wolfgang"
+    location: "Arbeitszimmer Wolfgang"
+    vendor: "eQ-3"
+    model: "MAX! Thermostat"
+    peer_id: "39"
+    channel: "1"
+```
+
+### Configuration Notes
+
+1. **technology**: Must be set to `"max"` to activate MAX! transformations
+2. **topics.set**: Use Homegear's `/set/` path with `/SET_TEMPERATURE` parameter
+3. **topics.state**: Use Homegear's `/plain/` path with `/SET_TEMPERATURE` parameter
+4. **features.current**: Set to `false` - SET_TEMPERATURE topic doesn't provide current temperature
+5. **metadata**: Include `peer_id` and `channel` for reference
+
+## Temperature Rounding
+
+MAX! only supports **integer temperatures**. The system uses standard rounding:
+
+| Abstract Input | MAX! Output |
+|----------------|-------------|
+| 20.4°C         | 20          |
+| 20.5°C         | 20          |
+| 20.6°C         | 21          |
+| 21.5°C         | 22          |
+| 22.5°C         | 22          |
+
+Python's `round()` function uses "banker's rounding" (round half to even).
+
+## Limitations
+
+1. **No current temperature**: SET_TEMPERATURE topic only reports target, not actual temperature
+2. **No mode control**: MAX! thermostats are always in heating mode
+3. **Integer only**: Temperature precision limited to 1°C steps
+4. **No battery status**: Not available via SET_TEMPERATURE topic
+5. **No window detection**: Not available via SET_TEMPERATURE topic
+
+## Testing
+
+Test the transformation functions:
+
+```bash
+poetry run python /tmp/test_max_transform.py
+```
+
+Expected output:
+```
+✅ PASS: Float 22.5 -> Integer string
+✅ PASS: Integer string -> Abstract dict
+✅ PASS: Integer -> Abstract dict
+✅ PASS: Rounding works correctly
+🎉 All MAX! transformation tests passed!
+```
+
+## Implementation Details
+
+### Files Modified
+
+1. **apps/abstraction/transformation.py**
+   - Added `_transform_thermostat_max_to_vendor()` - converts abstract → plain integer
+   - Added `_transform_thermostat_max_to_abstract()` - converts plain integer → abstract
+   - Registered handlers in `TRANSFORM_HANDLERS` registry
+
+2. **apps/abstraction/main.py**
+   - Modified `handle_abstract_set()` to send plain string for MAX! devices (not JSON)
+   - Modified message processing to handle plain text payloads from MAX! STATE topics
+
+### Transformation Functions
+
+```python
+def _transform_thermostat_max_to_vendor(payload: dict[str, Any]) -> str:
+    """Convert {"target": 22.5} → "22" """
+    target_temp = payload.get("target", 21.0)
+    return str(int(round(target_temp)))
+
+def _transform_thermostat_max_to_abstract(payload: str | int | float) -> dict[str, Any]:
+    """Convert "22" → {"target": 22.0, "mode": "heat"} """
+    target_temp = float(payload)
+    return {"target": target_temp, "mode": "heat"}
+```
+
+## Usage Example
+
+### Setting Temperature via API
+
+```bash
+curl -X POST http://localhost:8001/devices/thermostat_wolfgang/set \
+  -H "Content-Type: application/json" \
+  -d '{
+    "type": "thermostat",
+    "payload": {
+      "mode": "heat",
+      "target": 22.5
+    }
+  }'
+```
+
+**Flow:**
+1. API receives abstract payload: `{"mode": "heat", "target": 22.5}`
+2. Abstraction transforms to MAX!: `"22"`
+3. Publishes to: `homegear/instance1/set/39/1/SET_TEMPERATURE` with payload `22`
+
+### Receiving State Updates
+
+**Homegear publishes:**
+```
+Topic: homegear/instance1/plain/39/1/SET_TEMPERATURE
+Payload: 22
+```
+
+**Flow:**
+1. Abstraction receives plain text: `"22"`
+2. Transforms to abstract: `{"target": 22.0, "mode": "heat"}`
+3. Publishes to: `home/thermostat/thermostat_wolfgang/state`
+4. Publishes to Redis: `ui:updates` channel for real-time UI updates
+
+## Future Enhancements
+
+Potential improvements for better MAX! integration:
+
+1. **Current Temperature**: Subscribe to separate Homegear topic for actual temperature
+2. **Battery Status**: Subscribe to LOWBAT or battery level topics
+3. **Valve Position**: Monitor actual valve opening percentage
+4. **Window Detection**: Subscribe to window open detection status
+5. **Mode Control**: Support comfort/eco temperature presets
+
+## Related Documentation
+
+- [Homegear MAX! Documentation](https://doc.homegear.eu/data/homegear-max/)
+- [Abstract Protocol Specification](docs/PROTOCOL.md)
+- [Transformation Layer Design](apps/abstraction/README.md)
diff --git a/apps/abstraction/main.py b/apps/abstraction/main.py
index a05272a..f2e02ff 100644
--- a/apps/abstraction/main.py
+++ b/apps/abstraction/main.py
@@ -173,7 +173,12 @@ async def handle_abstract_set(
     # Transform abstract payload to vendor-specific format
     vendor_payload = transform_abstract_to_vendor(device_type, device_technology, abstract_payload)
     
-    vendor_message = json.dumps(vendor_payload)
+    # For MAX! thermostats, vendor_payload is a plain string (integer temperature)
+    # For other devices, it's a dict that needs JSON encoding
+    if device_technology == "max" and device_type == "thermostat":
+        vendor_message = vendor_payload  # Already a string
+    else:
+        vendor_message = json.dumps(vendor_payload)
     
     logger.info(f"→ vendor SET {device_id}: {vendor_topic} ← {vendor_message}")
     await mqtt_client.publish(vendor_topic, vendor_message, qos=1)
@@ -294,11 +299,30 @@ async def mqtt_worker(config: dict[str, Any], redis_client: aioredis.Redis) -> N
                     topic = str(message.topic)
                     payload_str = message.payload.decode()
                     
-                    try:
-                        payload = json.loads(payload_str)
-                    except json.JSONDecodeError:
-                        logger.warning(f"Invalid JSON on {topic}: {payload_str}")
-                        continue
+                    # Determine if message is from a MAX! device (requires plain text handling)
+                    is_max_device = False
+                    max_device_id = None
+                    max_device_type = None
+                    
+                    # Check if topic matches any MAX! device state topic
+                    for device_id, device in devices.items():
+                        if device.get("technology") == "max" and topic == device["topics"]["state"]:
+                            is_max_device = True
+                            max_device_id = device_id
+                            max_device_type = device["type"]
+                            break
+                    
+                    # Parse payload based on device technology
+                    if is_max_device:
+                        # MAX! sends plain integer/string, not JSON
+                        payload = payload_str.strip()
+                    else:
+                        # All other technologies use JSON
+                        try:
+                            payload = json.loads(payload_str)
+                        except json.JSONDecodeError:
+                            logger.warning(f"Invalid JSON on {topic}: {payload_str}")
+                            continue
                     
                     # Check if this is an abstract SET message
                     if topic.startswith("home/") and topic.endswith("/set"):
@@ -318,15 +342,24 @@ async def mqtt_worker(config: dict[str, Any], redis_client: aioredis.Redis) -> N
                     
                     # Check if this is a vendor STATE message
                     else:
-                        # Find device by vendor state topic
-                        for device_id, device in devices.items():
-                            if topic == device["topics"]["state"]:
-                                device_technology = device.get("technology", "unknown")
-                                await handle_vendor_state(
-                                    client, redis_client, device_id, device["type"], 
-                                    device_technology, payload, redis_channel
-                                )
-                                break
+                        # For MAX! devices, we already identified them above
+                        if is_max_device:
+                            device = devices[max_device_id]
+                            device_technology = device.get("technology", "unknown")
+                            await handle_vendor_state(
+                                client, redis_client, max_device_id, max_device_type, 
+                                device_technology, payload, redis_channel
+                            )
+                        else:
+                            # Find device by vendor state topic for other technologies
+                            for device_id, device in devices.items():
+                                if topic == device["topics"]["state"]:
+                                    device_technology = device.get("technology", "unknown")
+                                    await handle_vendor_state(
+                                        client, redis_client, device_id, device["type"], 
+                                        device_technology, payload, redis_channel
+                                    )
+                                    break
                         
         except asyncio.CancelledError:
             logger.info("MQTT worker cancelled")
diff --git a/apps/abstraction/transformation.py b/apps/abstraction/transformation.py
index 37516f9..964f8ff 100644
--- a/apps/abstraction/transformation.py
+++ b/apps/abstraction/transformation.py
@@ -124,6 +124,79 @@ def _transform_thermostat_zigbee2mqtt_to_abstract(payload: dict[str, Any]) -> di
     return payload
 
 
+# ============================================================================
+# HANDLER FUNCTIONS: max technology (Homegear MAX!)
+# ============================================================================
+
+def _transform_thermostat_max_to_vendor(payload: dict[str, Any]) -> str:
+    """Transform abstract thermostat payload to MAX! (Homegear) format.
+    
+    MAX! expects only the integer temperature value (no JSON).
+    
+    Transformations:
+    - Extract 'target' temperature from payload
+    - Convert float to integer (MAX! only accepts integers)
+    - Return as plain string value
+    
+    Example:
+    - Abstract: {'mode': 'heat', 'target': 22.5}
+    - MAX!: "22"
+    
+    Note: MAX! ignores mode - it's always in heating mode
+    """
+    if "target" not in payload:
+        logger.warning(f"MAX! thermostat payload missing 'target': {payload}")
+        return "21"  # Default fallback
+    
+    target_temp = payload["target"]
+    
+    # Convert to integer (MAX! protocol requirement)
+    if isinstance(target_temp, (int, float)):
+        int_temp = int(round(target_temp))
+        return str(int_temp)
+    
+    logger.warning(f"MAX! invalid target temperature type: {type(target_temp)}, value: {target_temp}")
+    return "21"
+
+
+def _transform_thermostat_max_to_abstract(payload: str | int | float) -> dict[str, Any]:
+    """Transform MAX! (Homegear) thermostat payload to abstract format.
+    
+    MAX! sends only the integer temperature value (no JSON).
+    
+    Transformations:
+    - Parse plain string/int value
+    - Convert to float for abstract protocol
+    - Wrap in abstract payload structure with mode='heat'
+    
+    Example:
+    - MAX!: "22" or 22
+    - Abstract: {'target': 22.0, 'mode': 'heat'}
+    
+    Note: MAX! doesn't send current temperature via SET_TEMPERATURE topic
+    """
+    try:
+        # Handle both string and numeric input
+        if isinstance(payload, str):
+            target_temp = float(payload.strip())
+        elif isinstance(payload, (int, float)):
+            target_temp = float(payload)
+        else:
+            logger.warning(f"MAX! unexpected payload type: {type(payload)}, value: {payload}")
+            target_temp = 21.0
+        
+        return {
+            "target": target_temp,
+            "mode": "heat"  # MAX! is always in heating mode
+        }
+    except (ValueError, TypeError) as e:
+        logger.error(f"MAX! failed to parse temperature: {payload}, error: {e}")
+        return {
+            "target": 21.0,
+            "mode": "heat"
+        }
+
+
 # ============================================================================
 # REGISTRY: Maps (device_type, technology, direction) -> handler function
 # ============================================================================
@@ -142,6 +215,8 @@ TRANSFORM_HANDLERS: dict[tuple[str, str, str], TransformHandler] = {
     ("thermostat", "simulator", "to_abstract"): _transform_thermostat_simulator_to_abstract,
     ("thermostat", "zigbee2mqtt", "to_vendor"): _transform_thermostat_zigbee2mqtt_to_vendor,
     ("thermostat", "zigbee2mqtt", "to_abstract"): _transform_thermostat_zigbee2mqtt_to_abstract,
+    ("thermostat", "max", "to_vendor"): _transform_thermostat_max_to_vendor,
+    ("thermostat", "max", "to_abstract"): _transform_thermostat_max_to_abstract,
 }