阻止来自其他设备的连接

I have a website and I just want mobile devices to enter the site.So my question is how can I block connections from other devices.

I'm able to use node.js html and php in my website.

You can use mobile detect class in PHP and then use a code like this :

// if visitor is not using any mobile device (phones or tablets).
if ( !$detect->isMobile() ) {
    die("access denied")
}