diff --git a/src/editor/components/ThemerComponent.js b/src/editor/components/ThemerComponent.js
index 8d3478a..6069d2b 100644
--- a/src/editor/components/ThemerComponent.js
+++ b/src/editor/components/ThemerComponent.js
@@ -1,4 +1,4 @@
-import { mergeWith, isEmpty } from 'lodash';
+import { mergeWith, isEmpty, isEqual } from 'lodash';
 import { Button, Spinner, TabPanel } from '@wordpress/components';
 import { useSelect, dispatch } from '@wordpress/data';
 import { useEffect, useState, useMemo } from '@wordpress/element';
@@ -36,12 +36,13 @@ const ThemerComponent = () => {
 		);
 	};
 
-	const { globalStylesId, baseConfig, userConfig } = useSelect(
-		( select ) => {
+	const { globalStylesId, baseConfig, userConfig, savedUserConfig } =
+		useSelect( ( select ) => {
 			const {
 				__experimentalGetCurrentGlobalStylesId,
 				__experimentalGetCurrentThemeBaseGlobalStyles,
 				getEditedEntityRecord,
+				getEntityRecord,
 			} = select( 'core' );
 
 			const currentGlobalStylesId =
@@ -55,9 +56,13 @@ const ThemerComponent = () => {
 					'globalStyles',
 					currentGlobalStylesId
 				),
+				savedUserConfig: getEntityRecord(
+					'root',
+					'globalStyles',
+					currentGlobalStylesId
+				),
 			};
-		}
-	);
+		} );
 
 	/**
 	 * Returns merged base and user configs
@@ -70,6 +75,13 @@ const ThemerComponent = () => {
 		return merged;
 	}, [ userConfig, baseConfig ] );
 
+	/**
+	 * Determines if the user config is different from the most recently saved config.
+	 */
+	const hasUnsavedChanges = useMemo( () => {
+		return ! isEqual( userConfig, savedUserConfig );
+	}, [ userConfig, savedUserConfig ] );
+
 	/**
 	 * Fetch new preview CSS whenever config is changed
 	 */
@@ -107,6 +119,20 @@ const ThemerComponent = () => {
 		validateThemeJson();
 	}, [] );
 
+	/**
+	 * Alert user if they try to leave Themer without saving.
+	 */
+	useEffect( () => {
+		// Detecting browser closing
+		window.onbeforeunload = hasUnsavedChanges
+			? () => hasUnsavedChanges
+			: null;
+
+		return () => {
+			window.removeEventListener( 'beforeunload', () => {} );
+		};
+	}, [ hasUnsavedChanges ] );
+
 	/**
 	 * saves edited entity data
 	 */
@@ -124,14 +150,14 @@ const ThemerComponent = () => {
 	};
 
 	/**
-	 * resets updated theme db data back to original theme.json
+	 * Resets theme db data back to the most recently saved config.
 	 */
 	const reset = () => {
 		dispatch( 'core' ).editEntityRecord(
 			'root',
 			'globalStyles',
 			globalStylesId,
-			baseConfig
+			savedUserConfig
 		);
 	};
 
@@ -169,11 +195,13 @@ const ThemerComponent = () => {
 									isSecondary
 									onClick={ () => reset() }
 									text="Reset"
+									disabled={ ! hasUnsavedChanges }
 								/>
 								<Button
 									isPrimary
 									onClick={ () => save() }
 									text="Save"
+									disabled={ ! hasUnsavedChanges }
 								/>
 							</div>
 							<div className="themer-body">