The not so good news is that many of them are expensive and, in their real-life form as commercial products, are not all that practical or necessary for an amateur spy.

There’s a few simple questions that any spy will need to consider before seizing on any one particular spy tactic:

• Do you need to identify actual content of a conversation, or is it enough to
  determine the identity of the people talking by hearing just a sampling of
  voices? Or perhaps even a recorded log of inbound and outbound phone
  numbers will suffice?
• Do you want to listen in to a conversation in “real time,” as it occurs, or
  are you able to entertain the (more convenient) option of recording calls
  and listening to them later?
• Do you have direct access to the phone or location you would like to tap
  into? Do you require a portable device that allows you to monitor multiple
  locations?
•  How much do you want to spend?

Short of building your own electronic devices – and there are plenty of hobbyist manuals available to this end – you should expect to fork out anywhere between $25 and $100 for some worthwhile equipment. These questions can help guide you toward the simplest and most potent spy arsenal for our own situation. Now let’s see what’s on offer…