For serious work, you shouldn’t identify Googlebot by just it’s UA as this is easily faked and there are tonnes of rougue crawlers in the wild pretending to be one. The proper way to identify a Googlebot should be using the double reverse DNS method and then use the UA to differentiate between desktop and mobile bots. Here’s an article on how to verify their bots. This method also works with other search engines. Just search for their appropriate articles.
We’ve used this method with high accuracy for the past few years and had even a custom system utilising MaxMind’s GeoIP2 Precision Services to gather insights on each visitor’s IP.
Here’s the current Googlebot smartphone UA according to Google’s blogpost. If you are familiar with them, you would notice that this is not the only smartphone UA albeit being the most used.
Mozilla/5.0 (iPhone; CPU iPhone OS 8_3 like Mac OS X) AppleWebKit/600.1.4 (KHTML, like Gecko) Version/8.0 Mobile/12F70 Safari/600.1.4 (compatible; Googlebot/2.1; +http://www.google.com/bot.html)
On 18th April onwards, it will be changed to
Mozilla/5.0 (Linux; Android 6.0.1; Nexus 5X Build/MMB29P) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/41.0.2272.96 Mobile Safari/537.36 (compatible; Googlebot/2.1; +http://www.google.com/bot.html)