Yes, you do it from Gumtree.
Start a search.
Filter it by all the criteria you require eg : region,price, model, km etc etc etc
Save the search.
If you've set up your Gumtree settings correctly you will now be notified every time an item that meets your criteria is listed.
I have it sending an email to my gmail account & I have my gmail setup on my phone.
The email has links to the adverts which you can click to be taken straight to the ad.
Although not really necessary, also have the Gumtree app on my phone.
As soon as I get a notification I can check the ad there & then & phone straightaway if necessary.
Hope this helps