diff --git a/check_home_assistant_state.py b/check_home_assistant_state.py
index 164d706..c468151 100755
--- a/check_home_assistant_state.py
+++ b/check_home_assistant_state.py
@@ -46,13 +46,31 @@ class ScalarOrUnknownContext(nagiosplugin.ScalarContext):
             )
 
 
+@dataclasses.dataclass
+class AttributeFilter:
+    attribute: str
+    value: str
+    negated: bool
+
+    @classmethod
+    def from_str(cls, arg: str):
+        k, _, v = arg.partition("=")
+        if k.endswith("!"):
+            return cls(k.removesuffix("!"), v, True)
+        else:
+            return cls(k, v, False)
+
+    def check(self, attributes: dict[str, str]) -> bool:
+        return self.negated ^ (attributes.get(self.attribute) == self.value)
+
+
 @dataclasses.dataclass
 class Entities(nagiosplugin.Resource):
     url: str
     token: str
     device_class: str
     numeric: bool
-    filters: list[str]
+    filters: list[AttributeFilter]
     attribute: Optional[str]
     friendly_name: bool
     ignore_missing: bool
@@ -122,7 +140,7 @@ class Entities(nagiosplugin.Resource):
         for state in response:
             if (
                 state["attributes"].get("device_class") == self.device_class
-                and all(state["attributes"].get(k) == v for k, v in self.filters)
+                and all(filter.check(state["attributes"]) for filter in self.filters)
                 and (len(self.include) == 0 or state["entity_id"] in self.include)
                 and state["entity_id"] not in self.exclude
             ):
@@ -169,11 +187,6 @@ class RegexContext(nagiosplugin.Context):
             )
 
 
-def key_value(arg: str):
-    k, _, v = arg.partition("=")
-    return k, v
-
-
 class Icinga2ConfAction(argparse.Action):
     def __init__(
         self,
@@ -302,10 +315,10 @@ def main():
     common_args.add_argument(
         "-f",
         "--filter",
-        type=key_value,
+        type=AttributeFilter.from_str,
         default=[],
         nargs="*",
-        help="filter by 'attribute=value' (may be specified multiple times)",
+        help="filter by 'attribute=value' (may be specified multiple times). Use != to negate the match",
     )
     common_args.add_argument(
         "-i",