wp_is_mobile()

function wp_is_mobile() {
	if ( empty($_SERVER['HTTP_USER_AGENT']) ) {
		$is_mobile = false;
	} elseif ( strpos($_SERVER['HTTP_USER_AGENT'], 'Mobile') !== false // many mobile devices (all iPhone, iPad, etc.)
		|| strpos($_SERVER['HTTP_USER_AGENT'], 'Android') !== false
		|| strpos($_SERVER['HTTP_USER_AGENT'], 'Silk/') !== false
		|| strpos($_SERVER['HTTP_USER_AGENT'], 'Kindle') !== false
		|| strpos($_SERVER['HTTP_USER_AGENT'], 'BlackBerry') !== false
		|| strpos($_SERVER['HTTP_USER_AGENT'], 'Opera Mini') !== false
		|| strpos($_SERVER['HTTP_USER_AGENT'], 'Opera Mobi') !== false ) {
			$is_mobile = true;
	} else {
		$is_mobile = false;
	}

	/**
	 * Filters whether the request should be treated as coming from a mobile device or not.
	 *
	 * @since WP-4.9.0
	 *
	 * @param bool $is_mobile Whether the request is from a mobile device or not.
	 */
	return apply_filters( 'wp_is_mobile', $is_mobile );
}