I am a dedicated detective. Even without the paraphenalia Sherlock wears. I own a copy of Idiot's Guide to Private Investigation. But I don't use my "skills" to find people alive. They've usually been in the ground or a small box, or in the wind, sea, or mountains. I'm a genealogist.
I use the same skills I used to obtain information for news articles when I was a budding journalist. I scare people with what I want to know. And they shut up tighter than the proverbial "Dick's hatband." So few folks today understand the importance of preserving family history. Sometimes I fall flat on my face with reasons why I want the information. Who has time, they say, to dredge up birth and death dates as well as family members of my grandparents? That happened too long ago! And I leave them searching for another member of the family from whom to draw the info. These are the ones who have never been asked family questions.
Keeping all information of your immediate family in one place, even a bank box, you will have ready for your family genealogist when she/he calls. his includes certificates of all types (birth, death, divorce,baptism,awards) letters, diaries,photographs, medals, and the like. Sounds like you need a special box to put them in? Indeed! Handwritten letters and notes are so special and fade with age that you need to make copies only a few times if any at all. Put them in UV ray-free enclosures you can purchase in a photography store. This careful attention as you age will be appreciated and easier to find at your passing.
A glance at www.ancestry.com (now advertised online and tv) to find a public search of your family is the beginning of a great treasure hunt. Only recently did I connect the Newkirks to families in New York, who had lived less than 100 miles from where we stay summers! How exciting now be able to plan a trip to visit cemeteries and place names where these elders once lived.
WARNING: This family checking can be habit-forming. When you find a long-lost great uncle or note which ship your great great grandfather sailed to the new world, you will have a whole new world of information to digest.