Make offers on "for sale by owners", on expired listings, get sellers to call you, advertise using print, radio and Internet.

Once that initial list is posted, I do a quick internet search on the homes (Most of the time I use county records and zillow/trulia simply because they are  at the top of the search).

You can knock on foreclosure doors, call Craigslist ads, search the internet, call realtors, get in the paper, send direct mail pieces to probate and out of state owners, etc. 

The sensor runs to a unit that I can control on the internet.  

Brian,If you are asking about internet based auctions then it would seem you would have alot more competition and I would only invest in high end properties and not invest more than the land is worth since you aren't physically looking at the properties to limit your risk.The better option is travel to a nearby state that is conducive for tax lien investing and do finish your due diligence by driving by the properties you are interested in.If you aren't careful you could invest potentially invest 15k or so in a property that looked good then it turns out to be worthless.If you had a family member or very close friend you could trust in a good tax lien investing state then you could get them to drive by the properties and you do the internet based research remotely.

All free on the Internet!

I was out of work most of that year and looking for opportunities.Of course, that was before the internet.

Right now I have 2 interns that are working with me for free and helping out with my internet marketing.

auction.com use your google on the Internet to explore homes on auctions

I have basic real estate knowledge from reading the Ultimate Beginner's Guide and other sources from the internet.