diff --git a/selfdrive/boardd/pigeon.cc b/selfdrive/boardd/pigeon.cc
index 3d9f25700d..d28b970694 100644
--- a/selfdrive/boardd/pigeon.cc
+++ b/selfdrive/boardd/pigeon.cc
@@ -41,7 +41,7 @@ Pigeon * Pigeon::connect(const char * tty){
   return pigeon;
 }
 
-bool Pigeon::wait_for_ack(std::string ack, std::string nack){
+bool Pigeon::wait_for_ack(const std::string &ack, const std::string &nack){
   std::string s;
   while (!do_exit){
     s += receive();
@@ -66,7 +66,7 @@ bool Pigeon::wait_for_ack(){
   return wait_for_ack(ack, nack);
 }
 
-bool Pigeon::send_with_ack(std::string cmd){
+bool Pigeon::send_with_ack(const std::string &cmd){
   send(cmd);
   return wait_for_ack();
 }
diff --git a/selfdrive/boardd/pigeon.h b/selfdrive/boardd/pigeon.h
index ff22042dc9..ecd42cb7b1 100644
--- a/selfdrive/boardd/pigeon.h
+++ b/selfdrive/boardd/pigeon.h
@@ -16,8 +16,8 @@ class Pigeon {
   void init();
   void stop();
   bool wait_for_ack();
-  bool wait_for_ack(std::string ack, std::string nack);
-  bool send_with_ack(std::string cmd);
+  bool wait_for_ack(const std::string &ack, const std::string &nack);
+  bool send_with_ack(const std::string &cmd);
   virtual void set_baud(int baud) = 0;
   virtual void send(const std::string &s) = 0;
   virtual std::string receive() = 0;
diff --git a/selfdrive/common/util.cc b/selfdrive/common/util.cc
index a7e1fe3a5b..6bd2913d08 100644
--- a/selfdrive/common/util.cc
+++ b/selfdrive/common/util.cc
@@ -76,7 +76,7 @@ std::string read_file(const std::string& fn) {
   return buffer.str();
 }
 
-int read_files_in_dir(std::string path, std::map<std::string, std::string> *contents) {
+int read_files_in_dir(const std::string &path, std::map<std::string, std::string> *contents) {
   DIR *d = opendir(path.c_str());
   if (!d) return -1;
 
diff --git a/selfdrive/common/util.h b/selfdrive/common/util.h
index 698ca819b5..697711a866 100644
--- a/selfdrive/common/util.h
+++ b/selfdrive/common/util.h
@@ -61,7 +61,7 @@ std::string dir_name(std::string const& path);
 
 // **** file fhelpers *****
 std::string read_file(const std::string& fn);
-int read_files_in_dir(std::string path, std::map<std::string, std::string>* contents);
+int read_files_in_dir(const std::string& path, std::map<std::string, std::string>* contents);
 int write_file(const char* path, const void* data, size_t size, int flags = O_WRONLY, mode_t mode = 0777);
 std::string readlink(const std::string& path);
 bool file_exists(const std::string& fn);
diff --git a/selfdrive/locationd/ublox_msg.h b/selfdrive/locationd/ublox_msg.h
index 965359d1c5..c314bc651e 100644
--- a/selfdrive/locationd/ublox_msg.h
+++ b/selfdrive/locationd/ublox_msg.h
@@ -46,7 +46,7 @@ namespace ublox {
     uint32_t tAccNs;
   } __attribute__((packed));
 
-  inline std::string ubx_add_checksum(std::string msg){
+  inline std::string ubx_add_checksum(const std::string &msg){
     assert(msg.size() > 2);
 
     uint8_t ck_a = 0, ck_b = 0;
diff --git a/selfdrive/ui/qt/offroad/networking.cc b/selfdrive/ui/qt/offroad/networking.cc
index 2b741a1fb7..ffb1b82c2c 100644
--- a/selfdrive/ui/qt/offroad/networking.cc
+++ b/selfdrive/ui/qt/offroad/networking.cc
@@ -106,7 +106,7 @@ void Networking::refresh(){
   an->refresh();
 }
 
-void Networking::connectToNetwork(Network n) {
+void Networking::connectToNetwork(const Network &n) {
   if (n.security_type == SecurityType::OPEN) {
     wifi->connect(n);
   } else if (n.security_type == SecurityType::WPA) {
@@ -115,7 +115,7 @@ void Networking::connectToNetwork(Network n) {
   }
 }
 
-void Networking::wrongPassword(QString ssid) {
+void Networking::wrongPassword(const QString &ssid) {
   for (Network n : wifi->seen_networks) {
     if (n.ssid == ssid) {
       QString pass = InputDialog::getText("Wrong password for \"" + n.ssid +"\"", 8);
diff --git a/selfdrive/ui/qt/offroad/networking.h b/selfdrive/ui/qt/offroad/networking.h
index 68a6d7c558..a9b3e2a325 100644
--- a/selfdrive/ui/qt/offroad/networking.h
+++ b/selfdrive/ui/qt/offroad/networking.h
@@ -36,7 +36,7 @@ private:
   bool tetheringEnabled;
 
 signals:
-  void connectToNetwork(Network n);
+  void connectToNetwork(const Network &n);
 
 public slots:
   void refresh();
@@ -81,8 +81,8 @@ private:
   void attemptInitialization();
 
 private slots:
-  void connectToNetwork(Network n);
+  void connectToNetwork(const Network &n);
   void refresh();
-  void wrongPassword(QString ssid);
+  void wrongPassword(const QString &ssid);
 };
 
diff --git a/selfdrive/ui/qt/offroad/wifiManager.cc b/selfdrive/ui/qt/offroad/wifiManager.cc
index a8d9e82982..747e587930 100644
--- a/selfdrive/ui/qt/offroad/wifiManager.cc
+++ b/selfdrive/ui/qt/offroad/wifiManager.cc
@@ -184,7 +184,7 @@ QList<Network> WifiManager::get_networks() {
   return r;
 }
 
-SecurityType WifiManager::getSecurityType(QString path) {
+SecurityType WifiManager::getSecurityType(const QString &path) {
   int sflag = get_property(path, "Flags").toInt();
   int wpaflag = get_property(path, "WpaFlags").toInt();
   int rsnflag = get_property(path, "RsnFlags").toInt();
@@ -202,22 +202,22 @@ SecurityType WifiManager::getSecurityType(QString path) {
   }
 }
 
-void WifiManager::connect(Network n) {
+void WifiManager::connect(const Network &n) {
   return connect(n, "", "");
 }
 
-void WifiManager::connect(Network n, QString password) {
+void WifiManager::connect(const Network &n, const QString &password) {
   return connect(n, "", password);
 }
 
-void WifiManager::connect(Network n, QString username, QString password) {
+void WifiManager::connect(const Network &n, const QString &username, const QString &password) {
   connecting_to_network = n.ssid;
   // disconnect();
   clear_connections(n.ssid); //Clear all connections that may already exist to the network we are connecting
   connect(n.ssid, username, password, n.security_type);
 }
 
-void WifiManager::connect(QByteArray ssid, QString username, QString password, SecurityType security_type) {
+void WifiManager::connect(const QByteArray &ssid, const QString &username, const QString &password, SecurityType security_type) {
   Connection connection;
   connection["connection"]["type"] = "802-11-wireless";
   connection["connection"]["uuid"] = QUuid::createUuid().toString().remove('{').remove('}');
@@ -243,7 +243,7 @@ void WifiManager::connect(QByteArray ssid, QString username, QString password, S
   activate_wifi_connection(QString(ssid));
 }
 
-void WifiManager::deactivate_connections(QString ssid) {
+void WifiManager::deactivate_connections(const QString &ssid) {
   for (QDBusObjectPath active_connection_raw : get_active_connections()) {
     QString active_connection = active_connection_raw.path();
     QDBusInterface nm(nm_service, active_connection, props_iface, bus);
@@ -279,7 +279,7 @@ QVector<QDBusObjectPath> WifiManager::get_active_connections() {
   return conns;
 }
 
-void WifiManager::clear_connections(QString ssid) {
+void WifiManager::clear_connections(const QString &ssid) {
   for(QDBusObjectPath path : list_connections()){
     QDBusInterface nm2(nm_service, path.path(), nm_settings_conn_iface, bus);
     nm2.setTimeout(dbus_timeout);
@@ -327,7 +327,7 @@ QString WifiManager::get_active_ap() {
   return r.path();
 }
 
-QByteArray WifiManager::get_property(QString network_path ,QString property) {
+QByteArray WifiManager::get_property(const QString &network_path , const QString &property) {
   QDBusInterface device_props(nm_service, network_path, props_iface, bus);
   device_props.setTimeout(dbus_timeout);
 
@@ -335,7 +335,7 @@ QByteArray WifiManager::get_property(QString network_path ,QString property) {
   return get_response<QByteArray>(response);
 }
 
-unsigned int WifiManager::get_ap_strength(QString network_path) {
+unsigned int WifiManager::get_ap_strength(const QString &network_path) {
   QDBusInterface device_props(nm_service, network_path, props_iface, bus);
   device_props.setTimeout(dbus_timeout);
 
@@ -409,7 +409,7 @@ QVector<QDBusObjectPath> WifiManager::list_connections(){
   return connections;
 }
 
-bool WifiManager::activate_wifi_connection(QString ssid){
+bool WifiManager::activate_wifi_connection(const QString &ssid){
   QString devicePath = get_adapter();
 
   for(QDBusObjectPath path : list_connections()){
@@ -514,7 +514,7 @@ bool WifiManager::tetheringEnabled() {
   return get_property(active_ap, "Ssid") == tethering_ssid;
 }
 
-void WifiManager::changeTetheringPassword(QString newPassword){
+void WifiManager::changeTetheringPassword(const QString &newPassword) {
   tetheringPassword = newPassword;
   clear_connections(tethering_ssid.toUtf8());
   addTetheringConnection();
diff --git a/selfdrive/ui/qt/offroad/wifiManager.h b/selfdrive/ui/qt/offroad/wifiManager.h
index bbbe2e3ed8..db60ac59bf 100644
--- a/selfdrive/ui/qt/offroad/wifiManager.h
+++ b/selfdrive/ui/qt/offroad/wifiManager.h
@@ -35,9 +35,9 @@ public:
   QString ipv4_address;
 
   void refreshNetworks();
-  void connect(Network ssid);
-  void connect(Network ssid, QString password);
-  void connect(Network ssid, QString username, QString password);
+  void connect(const Network &ssid);
+  void connect(const Network &ssid, const QString &password);
+  void connect(const Network &ssid, const QString &username, const QString &password);
   void disconnect();
 
   // Tethering functions
@@ -47,8 +47,8 @@ public:
 
   bool activate_tethering_connection();
   void addTetheringConnection();
-  bool activate_wifi_connection(QString ssid);
-  void changeTetheringPassword(QString newPassword);
+  bool activate_wifi_connection(const QString &ssid);
+  void changeTetheringPassword(const QString &newPassword);
 
 private:
   QVector<QByteArray> seen_ssids;
@@ -62,21 +62,21 @@ private:
   QString get_adapter();
   QString get_ipv4_address();
   QList<Network> get_networks();
-  void connect(QByteArray ssid, QString username, QString password, SecurityType security_type);
+  void connect(const QByteArray &ssid, const QString &username, const QString &password, SecurityType security_type);
   QString get_active_ap();
-  void deactivate_connections(QString ssid);
-  void clear_connections(QString ssid);
+  void deactivate_connections(const QString &ssid);
+  void clear_connections(const QString &ssid);
   QVector<QDBusObjectPath> get_active_connections();
   uint get_wifi_device_state();
-  QByteArray get_property(QString network_path, QString property);
-  unsigned int get_ap_strength(QString network_path);
-  SecurityType getSecurityType(QString ssid);
+  QByteArray get_property(const QString &network_path, const QString &property);
+  unsigned int get_ap_strength(const QString &network_path);
+  SecurityType getSecurityType(const QString &ssid);
   QVector<QDBusObjectPath> list_connections();
 
 private slots:
   void change(unsigned int new_state, unsigned int previous_state, unsigned int change_reason);
 signals:
-  void wrongPassword(QString ssid);
-  void successfulConnection(QString ssid);
+  void wrongPassword(const QString &ssid);
+  void successfulConnection(const QString &ssid);
   void refresh();
 };
diff --git a/selfdrive/ui/qt/widgets/setup.cc b/selfdrive/ui/qt/widgets/setup.cc
index c0b044273b..615b22b709 100644
--- a/selfdrive/ui/qt/widgets/setup.cc
+++ b/selfdrive/ui/qt/widgets/setup.cc
@@ -48,7 +48,7 @@ void PairingQRWidget::refresh(){
   this->updateQrCode(qrString);
 }
 
-void PairingQRWidget::updateQrCode(QString text) {
+void PairingQRWidget::updateQrCode(const QString &text) {
   QrCode qr = QrCode::encodeText(text.toUtf8().data(), QrCode::Ecc::LOW);
   qint32 sz = qr.getSize();
   // make the image larger so we can have a white border
diff --git a/selfdrive/ui/qt/widgets/setup.h b/selfdrive/ui/qt/widgets/setup.h
index 169dd594fd..81cb31680a 100644
--- a/selfdrive/ui/qt/widgets/setup.h
+++ b/selfdrive/ui/qt/widgets/setup.h
@@ -15,7 +15,7 @@ public:
 
 private:
   QLabel* qrCode;
-  void updateQrCode(QString text);
+  void updateQrCode(const QString &text);
   void showEvent(QShowEvent *event) override;
 
 private slots: