diff --git a/src/device/dsmr.rs b/src/device/dsmr.rs
index 3568700..510c2a7 100644
--- a/src/device/dsmr.rs
+++ b/src/device/dsmr.rs
@@ -3,6 +3,8 @@ use std::{
     time::Instant,
 };
 
+use crate::device::FormattableDevice;
+
 pub enum DsmrMessageType {
     Water,
     Gas,
@@ -34,8 +36,10 @@ impl DsmrState {
             last_seen: Instant::now(),
         }
     }
+}
 
-    pub fn format_open_metrics(&self) -> impl Display + '_ {
+impl FormattableDevice for DsmrState {
+    fn format_open_metrics(&self) -> impl Display + '_ {
         DsmrFormatter { device: self }
     }
 }
diff --git a/src/device/mitemp.rs b/src/device/mitemp.rs
index a7dd025..6ceb3ef 100644
--- a/src/device/mitemp.rs
+++ b/src/device/mitemp.rs
@@ -1,6 +1,6 @@
 use jzon::JsonValue;
 
-use crate::device::BDAddr;
+use crate::device::{BDAddr, FormattableDevice};
 use std::{
     fmt::{self, Debug, Display},
     time::Instant,
@@ -48,8 +48,10 @@ impl MiTempDevice {
             self.dew_point = dew_point;
         }
     }
+}
 
-    pub fn format_open_metrics(&self) -> impl Display + '_ {
+impl FormattableDevice for MiTempDevice {
+    fn format_open_metrics(&self) -> impl Display + '_ {
         MitempFormatter { device: self }
     }
 }
diff --git a/src/device/mod.rs b/src/device/mod.rs
index 614f66b..a1afedb 100644
--- a/src/device/mod.rs
+++ b/src/device/mod.rs
@@ -32,6 +32,10 @@ pub struct DeviceStates {
     active_rf_temp_id: RfDeviceId,
 }
 
+pub trait FormattableDevice {
+    fn format_open_metrics(&self) -> impl Display + '_;
+}
+
 impl DeviceStates {
     pub fn new(
         mi_temp_names: BTreeMap<BDAddr, String>,
@@ -44,12 +48,12 @@ impl DeviceStates {
         }
     }
 
-    pub fn devices(&self) -> impl Iterator<Item = (&Device, &DeviceState)> {
-        self.devices.iter()
+    pub fn devices(&self) -> impl Iterator<Item = &impl FormattableDevice> {
+        self.devices.values()
     }
 
-    pub fn dsmr_devices(&self) -> impl Iterator<Item = (&Device, &DsmrState)> {
-        self.dsmr_devices.iter()
+    pub fn dsmr_devices(&self) -> impl Iterator<Item = &impl FormattableDevice> {
+        self.dsmr_devices.values()
     }
 
     pub fn update(&mut self, device: Device, json: JsonValue) {
@@ -147,12 +151,12 @@ impl DeviceStates {
         }
     }
 
-    pub fn mi_temp(&self) -> impl Iterator<Item = (&BDAddr, &MiTempDevice)> {
-        self.mi_temp_devices.iter()
+    pub fn mi_temp(&self) -> impl Iterator<Item = &impl FormattableDevice> {
+        self.mi_temp_devices.values()
     }
 
-    pub fn rf_temp(&self) -> impl Iterator<Item = (&RfDeviceId, &TempState)> {
-        self.rf_temp_devices.iter()
+    pub fn rf_temp(&self) -> impl Iterator<Item = &impl FormattableDevice> {
+        self.rf_temp_devices.values()
     }
 
     pub fn retain(&mut self, cleanup_time: Instant, ping_time: Instant, client: &AsyncClient) {
diff --git a/src/device/rf.rs b/src/device/rf.rs
index 7077ef6..3726120 100644
--- a/src/device/rf.rs
+++ b/src/device/rf.rs
@@ -5,6 +5,8 @@ use std::str::FromStr;
 
 use serde::{Deserialize, Deserializer, de::Error};
 
+use crate::device::FormattableDevice;
+
 #[derive(Debug)]
 pub struct TempState {
     pub name: String,
@@ -22,8 +24,10 @@ impl TempState {
             humidity: 0,
         }
     }
+}
 
-    pub fn format_open_metrics(&self) -> impl Display + '_ {
+impl FormattableDevice for TempState {
+    fn format_open_metrics(&self) -> impl Display + '_ {
         TempFormatter { device: self }
     }
 }
diff --git a/src/device/tasmota.rs b/src/device/tasmota.rs
index 3fd880e..85937f3 100644
--- a/src/device/tasmota.rs
+++ b/src/device/tasmota.rs
@@ -5,6 +5,8 @@ use std::{
 
 use jzon::JsonValue;
 
+use crate::device::FormattableDevice;
+
 #[derive(Debug)]
 pub struct DeviceState {
     pub state: Option<bool>,
@@ -100,8 +102,10 @@ impl DeviceState {
             pms.update(&json["PMS5003"]);
         }
     }
+}
 
-    pub fn format_open_metrics(&self) -> impl Display + '_ {
+impl FormattableDevice for DeviceState {
+    fn format_open_metrics(&self) -> impl Display + '_ {
         TasmotaFormatter { device: self }
     }
 }
diff --git a/src/main.rs b/src/main.rs
index 983ed51..d6afec3 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -4,7 +4,7 @@ mod mqtt;
 mod topic;
 
 use crate::config::{Config, ListenConfig};
-use crate::device::{Device, DeviceStates};
+use crate::device::{Device, DeviceStates, FormattableDevice};
 use crate::mqtt::mqtt_stream;
 use crate::topic::Topic;
 use clap::Parser;
@@ -78,19 +78,19 @@ async fn serve(device_states: Arc<Mutex<DeviceStates>>, listen: ListenConfig) {
         .map(move |state: Arc<Mutex<DeviceStates>>| {
             let state = state.lock().unwrap();
             let mut response = String::new();
-            for (_, state) in state.devices() {
+            for state in state.devices() {
                 write!(&mut response, "{}", state.format_open_metrics())
                     .expect("formatting failed");
             }
-            for (_, state) in state.dsmr_devices() {
+            for state in state.dsmr_devices() {
                 write!(&mut response, "{}", state.format_open_metrics())
                     .expect("formatting failed");
             }
-            for (_, state) in state.mi_temp() {
+            for state in state.mi_temp() {
                 write!(&mut response, "{}", state.format_open_metrics())
                     .expect("formatting failed");
             }
-            for (_, state) in state.rf_temp() {
+            for state in state.rf_temp() {
                 write!(&mut response, "{}", state.format_open_metrics())
                     .expect("formatting failed");
             }