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Listening Devices
Back in the 1980s laser listening devices were the cutting edge of listening technology. They require that the conversation you're listening to be in a room with an exterior window, and that you can get a vantage point in a line directly across from the window. While that doesn't cover every situation, it works perfectly for meetings in hotel rooms, and most corporate espionage where you're listening in on corner office and boardroom conversations. I found a lovely DIY link.
The essence of it is a laser pointer, a cadmium sulphide photo cell, an old set of headphones and a cheap laptop computer. A tripod to put the laser pointer on is recommended, to keep things stable. The wires are snipped off the headphones and the leads connected to the photo cell. The jack is plugged in to laptop. The laser pointer is directed at the window in question. The laser bounces off the window and reflects back to near the source. The photocell is positioned to catch the reflected beam. The beam will produce an electrical signal which the laptop will pick up on its sound card.
Now, there are a couple of complications that need to be dealt with. The first is that people get suspicious if they see red dots coming through the window. Since laser sights for pistols and rifles are readily available and popular in movies, the suspicion could go to full blown panic pretty easily. The simple, low-tech solution is to point the laser at a section of the window concealed by curtains. A more high tech solution is to switch to an infrared laser, which isn't visible to the eye. Lining up the reflected beam is a little involved, it will require sweeping the photocell over the window until the signal is picked up.
The other problem is that there are background noises caused by things like passing trucks and loud stereos. In fact, the use of a loud stereo is a common technique to disrupt listening. Fortunately, computer processing power has made it easy to remove background noises with free software. White noise can also be added to the window by placing something against it that vibrates. If somebody suspects a laser listening device is going to be used, it can be foiled with duct tape and a marital aide.
Video Surveillance
Keeping an eye on a location can be difficult. People can't sit in cars all day without attracting attention, and resources for a proper stakeout require a decent sized team that can be spared from other activities. An inexpensive webcam can be positioned discretely to watch a location. Coupled with a wireless access point, it makes a discrete monitoring station.
Most common wireless access points can be modified in a couple of minutes to run a full blown operating system such as Linux or FreeBSD. Capture software can record images received from the camera. There is software designed for security systems that will only record frames that are different from the frames that came before. That reduces the amount of data to be recorded.
The camera gets placed, then the interested party swings by every day or two, parks on the street or in a back alley, and downloads the new images. They get most of the benefits of a surveillance team without needing to dedicate the resources for a full stakeout.
Tracking Devices
Cool tracking devices show up in spy movies and detective shows all the time. Free software that will project GPS data onto a map has been available for several years. Unfortunately inexpensive GPS devices aren't as readily available as might be desired. While they are built into phones, they aren't easy to extract and to interface with.
Garmin makes a GPS tracking system for hunting dogs that could be re-purposed for tracking anything else. The kit comes with a handheld unit which will show the direction to any of the devices registered to it, or a map of the course the dog has taken. Prices on the unit range from $350 to $650. That price can work for a team with financial resources, but is beyond a team on a shoestring budget.
