What is the senior technician likely using when she uses a pen-like device to lay along cables?

The senior technician is likely using a non-contact voltage detector when she employs a pen-like device along cables. This type of device is specifically designed to safely identify the presence of voltage without making direct contact with the conductor. The pen-like design allows for ease of use, enabling technicians to quickly and easily determine whether a cable is live and carrying voltage, which is crucial for ensuring safety during electrical work.

The device operates by sensing electric fields, thus providing a visual or audible indication of voltage presence, allowing technicians to work confidently around electrical systems. This is an essential tool in the technician’s toolkit, especially when troubleshooting or maintaining AV systems and other electrical installations.

The other options don’t fit as closely with the context of a pen-like device in use. While recording modulated signals is a task associated with specific testing equipment, it doesn't match the described action. Making invisible cable markers typically involves other methods like printable labels or physical markers rather than a pen-like tool used for voltage detection. Charging a USB backup battery would involve different equipment entirely and would not utilize a pen-like device in the context described.