They already exist and most major militaries have both ground and air based (on fighter jets) infrared search and track. Main limitation is that the atmosphere and weather can attenuate infrared, and that it's a camera system, so range is limited by those factors compared to radar. It's also why it's more common on aircraft (air is thinner and colder at altitude). This also means tracking lots of targets, especially at longer ranges, is complex if only infrared is used. A laser rangefinder is usually added to the system to obtain distance data, and engagement range is usually around two thirds of detection range.
https://www.aeroflap.com.br/en/USAF-f-15c-fires-first-aim-120-missile-guided-by-irst/
As for infrared systems likely in use in Yemen, there's the Iranian Sepehr-14 fire control system, designed to link up with the Iranian Raad air defence system that can fire Sayyad 2C surface to air missiles. The Raad firing Sayyad 2C missiles is a capabilitiy that Ansarallah likely already have, given intercepted shipments of Sayyad 2C missiles to Yemen. You can see the camera array here.
If you want a serious answer, it's probably Kristi Noem, DHS Secretary.