Want to Spy on Somebody? It's Easier Than Ever

All in one smartphone and PC monitoring device.
Source: SpyTec
All in one smartphone and PC monitoring device.

The iconic private eye of film noir would not get very far using traditional detective methods in the era of communicating by smart phones and the Internet, when there's no paper to leave a trail.

With current technology, a gumshoe need not even wear shoes, nor does an investigation necessarily require a professional investigator. Many options are available to anybody who wants to know what someone else is doing in the digital realm.

Keystroke loggers record everything that's typed on the designated computer or mobile device. They are installed as software such as Web Watcher, which leaves no visible files on the computer. In the case of Web Watcher, the program sends the information to a web-based account. It can report on email, social media, web history, searches, the computer's location, as well as the programs are being used, and the person monitoring the computer can set up alert words to trigger screenshots.

If the person installing that keystroke logging software needs to log in but doesn't have that computer's password, it's a matter of making another purchase: a password cracking utility.

(Read more: Former U.S. Spy Warns on Cybersecurity)

For smart phones, there are flash drives such as the Recover It that can pull deleted emails, videos, or pictures, search chat logs, or Cellphone Recon, which can show the user all phone calls made, GPS locations of the phone, text messages and emails, and Internet browsing history. Once installed, it's running whenever the phone is on, but the application does not show up on the mobile device as a running program.

Cellphone Recon allows you easily and covertly monitor all cellphone activity.
Source: SpyTec
Cellphone Recon allows you easily and covertly monitor all cellphone activity.

There are many smart phone apps for functions such as covert audio and phone call recordings, covert photo and video recordings, sending messages that self-destruct, and for GPS location tracking.

Now, all of these products and services surely raise legal and ethical concerns. It mostly hinges on how you use them. Legitimate reasons include monitoring your children's online behavior to protect their safety, monitoring employee behavior while on the job, and in the case of the keystroke loggers, making sure no one is using your computer while you're away.

Jon Mark, owner of the SpyTec store in New York, which sells some of the smart phone and computer monitoring devices, said, "Our products are like anything else … a car or a steak knife. You can use a car to go from one place to the other, or feloniously. Our stuff you can use for good, important purposes, or you can use it to be … almost criminal."

SpyTec is a 10-year-old midtown shop that does about three- quarters of its business online. It typically sells nanny cams to parents, and granny cams to monitor eldercare-givers, as well as supplying customers with spousal fidelity concerns, private investigators and police detectives. In more recent years, Mark has seen a shift toward the digital spying methods, which he says is still a growing segment of his business but makes up about 25 percent of it now. He notes he doesn't sell any voice recording devices since covertly recording audio is illegal in most states.

He said the biggest sellers are the smartphone devices, "since most people seem to use them as their main avenue of communication these days."

(Read more: US to Let Spy Agencies Scour Americans' Finances)

For those not inclined to conduct their own investigations of communications and activities that are presumed private, many people offer worlds of information while using the Internet to anyone who cares to look. Shellee Hale, private investigator and president of Camandago, offers "Internet Investigations" as well as email tracing and investigation of the subject's Internet footprint.

"We have the World Wide Web and the invisible web: things that are behind firewalls, password protected," Hale said. "How do you get to that without just doing Google?"

"It used to be that 60 to 80 percent of web material was not being crawled by spiders [for indexing in Google's search results]. There are techniques you can use if you're a [webpage] owner to not have it crawl certain pages. There's also techniques you can use to search those pages." Hale cites Webferret, Websleuth, Centerfuge, Infomine and the Wayback Machine, programs and sites available to anyone, as her investigative tools.

"As a private person, the access to data is often so great you don't need to pull a private investigator, you can do it yourself if you get a little education and do research around it."