Spy listening devices include phone bugs, tiny microphones and sound magnifying devices. Tiny listening devices can be hidden and can pick up sound when people speak near them. Investigators can place a sound magnifier a distance away from the sound — but still within the line of sight — and still hear what is being said. Wall microphones can be placed against the wall so that a person can hear conversations in the next room.

Phone bugs are popular spy listening devices, and they are often seen in the movies. They usually have been found on traditional land-line phones, but cell phones also can be bugged. These bugs allow spies to hear conversations made through the phone, and some can also serve double-duty as a device to monitor a person's whereabouts.

Tiny spy microphones can be placed on lapels or hidden in other areas of clothing to pick up sounds at close range. Spy devices such as pens with covert recording devices are also used. Recording devices can also be placed in fire alarms or clocks, which appear to be ordinary objects but contain hidden spy listening devices. They typically are placed in areas where the target will likely approach. Some of these listening devices do not begin recording until they pick up sound.

Spies and detectives can use a sound magnifying device to hear conversations as far as 300 feet (91.44 m) away. These spy listening devices are large devices that are used for long distance hearing. Hunters also use the sound magnifiers to find out when animals are near.

Some sound magnifiers have recording devices and equalizers to adjust sound levels. The magnifying devices are battery-operated for use in remote areas. These are prime tools for listening when a detective cannot risk a close encounter with the target.

Wall microphones allow people to hear conversations in through the walls. Some models can detect sounds through steel. To use the wall microphones, spies place the equipment on a flat surface and listen. The volume can be adjusted to amplify quieter voices. Wall microphones can be used to hear what is going on in closed meetings and can be used to hear through ceilings or floors as well as walls.

Spy listening devices are sold online as well as some specialty shops. Customers include law enforcement officials, who use listening devices to help catch criminals. Hunters can use outdoor models to locate and hunt animals. Husbands, wives or people who are in relationships also might use these devices if they suspect that their partner is cheating in the relationship or is engaging in some other type of questionable or risky activity, such as problem gambling or substance abuse. Many places have laws that restrict the use of listening devices, so one should be careful to learn the local laws before using spy listening devices.