wp_password_change_notification( WP_User $user )

function wp_password_change_notification( $user ) {
	// send a copy of password change notification to the admin
	// but check to see if it's the admin whose password we're changing, and skip this
	if ( 0 !== strcasecmp( $user->user_email, get_option( 'admin_email' ) ) ) {
		/* translators: %s: user name */
		$message = sprintf( __( 'Password changed for user: %s' ), $user->user_login ) . "\r\n";
		// The blogname option is escaped with esc_html on the way into the database in sanitize_option
		// we want to reverse this for the plain text arena of emails.
		$blogname = wp_specialchars_decode(get_option('blogname'), ENT_QUOTES);

		$wp_password_change_notification_email = array(
			'to'      => get_option( 'admin_email' ),
			/* translators: Password change notification email subject. %s: Site title */
			'subject' => __( '[%s] Password Changed' ),
			'message' => $message,
			'headers' => '',
		);

		/**
		 * Filters the contents of the password change notification email sent to the site admin.
		 *
		 * @since WP-4.9.0
		 *
		 * @param array   $wp_password_change_notification_email {
		 *     Used to build wp_mail().
		 *
		 *     @type string $to      The intended recipient - site admin email address.
		 *     @type string $subject The subject of the email.
		 *     @type string $message The body of the email.
		 *     @type string $headers The headers of the email.
		 * }
		 * @param WP_User $user     User object for user whose password was changed.
		 * @param string  $blogname The site title.
		 */
		$wp_password_change_notification_email = apply_filters( 'wp_password_change_notification_email', $wp_password_change_notification_email, $user, $blogname );

		wp_mail(
			$wp_password_change_notification_email['to'],
			wp_specialchars_decode( sprintf( $wp_password_change_notification_email['subject'], $blogname ) ),
			$wp_password_change_notification_email['message'],
			$wp_password_change_notification_email['headers']
		);
	}
}