How to stop my google searches from showing up on all of my devices.

I've googled this question extentinsively without any success,so I thought I'd try here. I have an andriod and a tablet (both connected to my gmail account. When I google search on my phone I notice that the searches are on my tablet too. Normally this wouldn't bother me, but other people use my tablet too. (family) and when I Google and buy gifts for them online, I would like for them to be suprised. How can I stop this?