Here is the study (pdf, 16 pages): https://www.usenix.org/system/files/usenixsecurity23-ceccio.pdf

TLDR:

• Spy devices are available, effective, easy to find and affordable. Using simple searches on popular retailers in the US (the researchers studied Amazon, eBay, Best Buy, Walmart and Home Depot, all of which are located in the U.S., though some with a global presence), retailers often guide searching for such products through query completion, for example “catch a cheater” query is completed on Amazon with “catch a cheater spy devices car.” Many of the almost 3,000 devices can be purchased for under $50.

• Almost all of the devices are capable of Intimate Partner Surveillance (IPS). Generally, an abuser and a survivor of IPS are either living together or living apart. When the abuser and survivor are living together, the abuser has access to the survivor’s physical surroundings and belongings. Therefore, the abuser can even use devices that require regular retrieval, such as devices that rely on rechargeable bat- teries or devices that record exclusively to an SD card. These devices are much harder to detect compared to devices relying on wireless communication. When the abuser and survivor are living apart, the abuser can still continue conducting IPS using devices that use WiFi or 4G.

• Current detection tools are not up to the task of detecting the spy devices available to abusers. Devices that don’t use WiFi, such as LTE GPS trackers or cameras that only use local storage, cannot be detected and localized with any current technique. Finally, WiFi devices that are not streaming are also difficult to localize with current technologies.

• The spy devices can be categorized into four groups based on the communication technology they rely on for data transmission: WiFi, BLE, LTE, and no transmission / local storage. Detection solutions are therefore required for all of these categories, as all four types of devices have the potential to be used for IPS.

• The researchers encourage the research community to expand upon existing detection techniques while ensuring these techniques are usable for average people, and they suggest that online retailers and lawmakers should put rules in place that curtail the sale of devices intended to enable IPS to protect vulnerable populations.