diff --git a/src/lib/key-functions.c b/src/lib/key-functions.c
index 53c6011..48517b6 100644
--- a/src/lib/key-functions.c
+++ b/src/lib/key-functions.c
@@ -18,78 +18,102 @@
 
 #include "key-functions.h"
 
+// ----------------------------------------------------------------------------
 
-void kbfun_press( KBFUN_FUNCTION_ARGS ) {
+/*
+ * Generate a normal keypress or keyrelease
+ *
+ * Arguments
+ * - keycode: the keycode to use
+ * - pressed: whether to generate a keypress (true) or keyrelease (false)
+ *
+ * Note
+ * - Because of the way USB does things, what this actually does is either add
+ *   or remove 'keycode' from the list of currently pressed keys
+ */
+static void _press_release(uint8_t keycode, bool pressed) {
 	// no-op
-	if (keycode_ == 0)
+	if (keycode == 0)
 		return;
 
 	// modifier keys
-	switch (keycode_) {
-		case KEY_LeftControl:  keyboard_modifier_keys |= (1<<0);
+	switch (keycode) {
+		case KEY_LeftControl:  (pressed)
+				       ? (keyboard_modifier_keys |=  (1<<0))
+				       : (keyboard_modifier_keys &= ~(1<<0));
 				       return;
-		case KEY_LeftShift:    keyboard_modifier_keys |= (1<<1);
+		case KEY_LeftShift:    (pressed)
+				       ? (keyboard_modifier_keys |=  (1<<1))
+				       : (keyboard_modifier_keys &= ~(1<<1));
 				       return;
-		case KEY_LeftAlt:      keyboard_modifier_keys |= (1<<2);
+		case KEY_LeftAlt:      (pressed)
+				       ? (keyboard_modifier_keys |=  (1<<2))
+				       : (keyboard_modifier_keys &= ~(1<<2));
 				       return;
-		case KEY_LeftGUI:      keyboard_modifier_keys |= (1<<3);
+		case KEY_LeftGUI:      (pressed)
+				       ? (keyboard_modifier_keys |=  (1<<3))
+				       : (keyboard_modifier_keys &= ~(1<<3));
 				       return;
-		case KEY_RightControl: keyboard_modifier_keys |= (1<<4);
+		case KEY_RightControl: (pressed)
+				       ? (keyboard_modifier_keys |=  (1<<4))
+				       : (keyboard_modifier_keys &= ~(1<<4));
 				       return;
-		case KEY_RightShift:   keyboard_modifier_keys |= (1<<5);
+		case KEY_RightShift:   (pressed)
+				       ? (keyboard_modifier_keys |=  (1<<5))
+				       : (keyboard_modifier_keys &= ~(1<<5));
 				       return;
-		case KEY_RightAlt:     keyboard_modifier_keys |= (1<<6);
+		case KEY_RightAlt:     (pressed)
+				       ? (keyboard_modifier_keys |=  (1<<6))
+				       : (keyboard_modifier_keys &= ~(1<<6));
 				       return;
-		case KEY_RightGUI:     keyboard_modifier_keys |= (1<<7);
+		case KEY_RightGUI:     (pressed)
+				       ? (keyboard_modifier_keys |=  (1<<7))
+				       : (keyboard_modifier_keys &= ~(1<<7));
 				       return;
 	}
 
 	// all others
-	for (uint8_t i=0; i<6; i++)
-		if (keyboard_keys[i] == 0) {
-			keyboard_keys[i] = keycode_;
-			return;
+	for (uint8_t i=0; i<6; i++) {
+		if (pressed) {
+			if (keyboard_keys[i] == 0) {
+				keyboard_keys[i] = keycode;
+				return;
+			}
+		} else {
+			if (keyboard_keys[i] == keycode) {
+				keyboard_keys[i] = 0;
+				return;
+			}
 		}
+	}
 }
 
+// ----------------------------------------------------------------------------
+
+/*
+ * - press
+ * - generate a normal keypress
+ */
+void kbfun_press( KBFUN_FUNCTION_ARGS ) {
+	_press_release(keycode_, true);
+}
+
+/*
+ * - release
+ * - generate a normal keyrelease
+ */
 void kbfun_release( KBFUN_FUNCTION_ARGS ) {
-	// no-op
-	if (keycode_ == 0)
-		return;
-
-	// modifier keys
-	switch (keycode_) {
-		case KEY_LeftControl:  keyboard_modifier_keys &= ~(1<<0);
-				       return;
-		case KEY_LeftShift:    keyboard_modifier_keys &= ~(1<<1);
-				       return;
-		case KEY_LeftAlt:      keyboard_modifier_keys &= ~(1<<2);
-				       return;
-		case KEY_LeftGUI:      keyboard_modifier_keys &= ~(1<<3);
-				       return;
-		case KEY_RightControl: keyboard_modifier_keys &= ~(1<<4);
-				       return;
-		case KEY_RightShift:   keyboard_modifier_keys &= ~(1<<5);
-				       return;
-		case KEY_RightAlt:     keyboard_modifier_keys &= ~(1<<6);
-				       return;
-		case KEY_RightGUI:     keyboard_modifier_keys &= ~(1<<7);
-				       return;
-	}
-
-	// all others
-	for (uint8_t i=0; i<6; i++)
-		if (keyboard_keys[i] == keycode_) {
-			keyboard_keys[i] = 0;
-			return;
-		}
+	_press_release(keycode_, false);
 }
 
 // TODO:
-// - implement two shifts => capslock
 // - implement layer lock key combos (make a function to switch to a specific
 //   layer)
 
+/*
+ * - next layer
+ * - layer increment (for all keys)
+ */
 void kbfun_layer_inc( KBFUN_FUNCTION_ARGS ) {
 	for (uint8_t row=0; row<KB_ROWS; row++)
 		for (uint8_t col=0; col<KB_COLUMNS; col++)
@@ -98,6 +122,10 @@ void kbfun_layer_inc( KBFUN_FUNCTION_ARGS ) {
 			// else do nothing
 }
 
+/*
+ * - previous layer
+ * - layer decrement (for all keys)
+ */
 void kbfun_layer_dec( KBFUN_FUNCTION_ARGS ) {
 	for (uint8_t row=0; row<KB_ROWS; row++)
 		for (uint8_t col=0; col<KB_COLUMNS; col++)
@@ -106,3 +134,20 @@ void kbfun_layer_dec( KBFUN_FUNCTION_ARGS ) {
 			// else do nothing
 }
 
+/*
+ * - two keys => capslock
+ * - when assigned to two keys (e.g. the physical left and right shift keys),
+ *   pressing and holding down one of them makes the second toggle capslock
+ */
+void kbfun_2_keys_capslock_press_release( KBFUN_FUNCTION_ARGS ) {
+	static uint8_t keys_pressed = 0;
+
+	if (!pressed_) keys_pressed--;
+
+	_press_release(keycode_, pressed_);
+	if (keys_pressed == 1)
+		_press_release(KEY_CapsLock, pressed_);
+
+	if (pressed_) keys_pressed++;
+}
+
diff --git a/src/lib/key-functions.h b/src/lib/key-functions.h
index b709474..7b80874 100644
--- a/src/lib/key-functions.h
+++ b/src/lib/key-functions.h
@@ -35,7 +35,7 @@
 
 
 	#define KBFUN_FUNCTION_ARGS					\
-		uint8_t keycode_,					\
+		uint8_t keycode_, bool pressed_,			\
 		uint8_t (*current_layers_)[KB_ROWS][KB_COLUMNS],	\
 		uint8_t (*pressed_layers_)[KB_ROWS][KB_COLUMNS],	\
 		uint8_t * row_, uint8_t * col_
diff --git a/src/main.c b/src/main.c
index 340873a..56ea6b5 100644
--- a/src/main.c
+++ b/src/main.c
@@ -64,6 +64,7 @@ int main(void) {
 						if (press_function) {
 							(*press_function)(
 									kb_layout_get(current_layer, row, col),
+									true,
 									&current_layers, &pressed_layers,
 									&row, &col );
 						}
@@ -75,6 +76,7 @@ int main(void) {
 						if (release_function) {
 							(*release_function)(
 									kb_layout_get(pressed_layer, row, col),
+									false,
 									&current_layers, &pressed_layers,
 									&row, &col );
 						}