Speakers and microphones with a frequency response of 20kHz are required to successfully play/listen for LISNR Tones.
Most commodity speakers are easily able to produce the signal. Depending on your environment and quality of hardware, there are models that might perform better than others for your use case.
The LISNR team performs internal testing with speakers selected from the following site: https://www.rtings.com/speaker/0-8/graph#18516/4553 This site provides graphs of frequency response ranges (most important that there are data points in the 18kHz-20kHz range), directivity, and dynamic range compression for different commercial speakers that can be used for testing. Given that budgets and directivity goals for test equipment vary between our customers, this will provide a range of devices in different price ranges. Ex. the Echo Gen 4 is a lower budget speaker ($60) from this site, but some of the higher budget speakers that have more positive frequency responses in the ultrasonic range are: JBL Boombox 2 & 3, Bose Portable Smart Speaker, Soundboks (Gen3), Sonos One SL.