Maybe did you forgot what you were doing last week? Even if you do, you probably don’t know exactly what you where doing last summer.
(Un)fortunately, your friend Google can help you. You may already know it (or not) but Google keep track of all you movements (if you use their services and clicked « Yes » when they ask for your permission). If you have activated Google now or Google map using your Google account, George Orwell’s 1984 and his Big Brother seems to be an optimistic view of the actual reallity. But, as nothing is always black or white, especially in risk management, this invasion in your privacy might help you remember where you were last summer. Google does not advertise it so much but you can see all your history of location (if you have allowed them to do so) on the location history map on https://maps.google.com/locationhistory/.
You can use it to relive your hollidays using Streetview , find where you were at a specifi date and time, check the number of kilometers you drove on a specific day.
Of course you can imagine the amount of information you can gather if this system start to keep track also of all the network nearby, the blutotth devices visible at a specific time, the NFC payment you or the sound heard by your phone (yes, remember Google Now wait for you « OK Google » and is thus listening continuously when it run).
Get alarmed or don’t, at least, now, you know it.