diff --git a/src/config.rs b/src/config.rs
index e76f590..3f4b2d8 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -2,7 +2,7 @@ use std::error::Error;
 use std::fs;
 
 pub fn load_config(filename: &str) -> Result<Config, Box<dyn Error>> {
-    let yaml = fs::read_to_string(&filename).unwrap();
+    let yaml = fs::read_to_string(&filename)?;
     println!("{}", yaml.len());
     return Ok(Config { modmap: vec![], keymap: vec![] })
 }
diff --git a/src/input.rs b/src/input.rs
index 19cfdca..f69cbb2 100644
--- a/src/input.rs
+++ b/src/input.rs
@@ -1,9 +1,10 @@
 extern crate evdev;
 
 use evdev::Device;
+use std::error::Error;
 
-pub fn select_device() -> Device {
+pub fn select_device() -> Result<Device, Box<dyn Error>> {
     // TODO: stop hard-coding the device
-    let device = Device::open("/dev/input/event19");
-    return device.unwrap();
+    let device = Device::open("/dev/input/event19")?;
+    return Ok(device);
 }
diff --git a/src/main.rs b/src/main.rs
index 7d0bc37..3605f00 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,4 +1,4 @@
-use evdev::{Device, EventType};
+use evdev::{EventType};
 use std::error::Error;
 use std::env;
 use std::process::exit;
@@ -9,24 +9,30 @@ mod select;
 mod transform;
 mod config;
 
-fn event_loop(input_device: &mut Device) -> Result<(), Box<dyn Error>> {
-    let mut output_device = output::build_device(input_device).unwrap();
+fn event_loop() -> Result<(), Box<dyn Error>> {
+    let mut input_device = input::select_device()
+        .map_err(|e| format!("Failed to open an input device: {}", e))?;
+    let mut output_device = output::build_device(&input_device)
+        .map_err(|e| format!("Failed to build an output device: {}", e))?;
+    input_device.grab()
+        .map_err(|e| format!("Failed to grab an input device: {}", e))?;
+
     loop {
-        if !select::is_readable(input_device) {
+        if !select::is_readable(&mut input_device)? {
             continue;
         }
 
-        for event in input_device.fetch_events().unwrap() {
+        for event in input_device.fetch_events()? {
             if event.event_type() == EventType::KEY {
-                transform::on_event(event, &mut output_device);
+                transform::on_event(event, &mut output_device)?;
             } else {
-                output_device.emit(&[event]).unwrap();
+                output_device.emit(&[event])?;
             }
         }
     }
 }
 
-fn main() -> Result<(), Box<dyn Error>> {
+fn main() {
     let filename = match env::args().nth(1) {
         Some(filename) => filename,
         None => {
@@ -41,11 +47,13 @@ fn main() -> Result<(), Box<dyn Error>> {
             exit(1);
         },
     };
-    println!("{:?}", config);
+    println!("{:#?}", config);
 
-    let mut device = input::select_device();
-    device.grab()?;
-    event_loop(&mut device)?;
-    device.ungrab()?;
-    Ok(())
+    match event_loop() {
+        Ok(()) => {},
+        Err(e) => {
+            println!("Error: {}", e);
+            exit(1);
+        },
+    }
 }
diff --git a/src/output.rs b/src/output.rs
index 862b4a2..100e8b2 100644
--- a/src/output.rs
+++ b/src/output.rs
@@ -3,10 +3,10 @@ use evdev::{Device};
 use std::error::Error;
 
 pub fn build_device(base_device: &Device) -> Result<VirtualDevice, Box<dyn Error>> {
-    let device = VirtualDeviceBuilder::new()?
-        .name("xremap")
-        .with_keys(base_device.supported_keys().unwrap())?
-        .build()
-        .unwrap();
+    let builder = VirtualDeviceBuilder::new()?.name("xremap");
+    let device = match base_device.supported_keys() {
+        Some(keys) => builder.with_keys(keys)?,
+        None => builder,
+    }.build()?;
     Ok(device)
 }
diff --git a/src/select.rs b/src/select.rs
index b661343..c1b00d2 100644
--- a/src/select.rs
+++ b/src/select.rs
@@ -3,10 +3,11 @@ extern crate evdev;
 use evdev::Device;
 use std::os::unix::io::{AsRawFd, RawFd};
 use std::{io, mem, ptr};
+use std::error::Error;
 
 // A call of this function blocks until the argument device becomes readable.
 // TODO: support selecting multiple devices
-pub fn is_readable(device: &mut Device) -> bool {
+pub fn is_readable(device: &mut Device) -> Result<bool, Box<dyn Error>> {
     let mut fd_set = FdSet::new(); // TODO: maybe this should be prepared in the caller
     fd_set.set(device.as_raw_fd());
 
@@ -21,9 +22,8 @@ pub fn is_readable(device: &mut Device) -> bool {
     } {
         -1 => Err(io::Error::last_os_error()),
         res => Ok(res as usize),
-    }
-    .unwrap();
-    return result == 1 && fd_set.is_set(device.as_raw_fd());
+    }?;
+    return Ok(result == 1 && fd_set.is_set(device.as_raw_fd()));
 }
 
 fn to_fdset_ptr(opt: Option<&mut FdSet>) -> *mut libc::fd_set {
diff --git a/src/transform.rs b/src/transform.rs
index 6417851..f0328dd 100644
--- a/src/transform.rs
+++ b/src/transform.rs
@@ -1,13 +1,15 @@
+use std::error::Error;
 use evdev::{EventType, InputEvent, InputEventKind};
 use evdev::uinput::VirtualDevice;
 
-pub fn on_event(event: InputEvent, device: &mut VirtualDevice) {
+pub fn on_event(event: InputEvent, device: &mut VirtualDevice) -> Result<(), Box<dyn Error>> {
     println!("event: {:?}", event);
     if event.kind() == InputEventKind::Key(evdev::Key::KEY_A) {
         device.emit(&[
             InputEvent::new(EventType::KEY, evdev::Key::KEY_B.code(), event.value())
-        ]).unwrap();
+        ])?;
     } else {
-        device.emit(&[event]).unwrap();
+        device.emit(&[event])?;
     }
+    Ok(())
 }