What different technical variants are available for eavesdropping? Where are bugs placed? What are the possibilities for intercepting traditional telephone traffic or calls over GSM mobile networks? What techniques can be applied to monitor computers and internet activities? And not to forget, how can the target person be visually investigated with video surveillance? Techniques are used for this, which are also employed in authorized large-scale eavesdropping operations. They are freely available, increasingly cost-effective, and easier to use. Their sale and purchase are permitted, but their application is often not allowed in many countries. When used in close proximity, they can only be located and neutralized after targeted searching, making them largely risk-free to use. Eavesdropping technology appears in various forms in daily practice. In addition to purely acoustic listening devices, there are also electroacoustic listening devices and audiovisual surveillance systems. There are also various technical solutions for tapping phones. Listening to a cell phone is easier today than one might think, with corresponding software solutions available to everyone. We provide you with the information for this in this blog.