Some sort of software analysis performed by SoundThinking identifies a possible gunshot. The audio recordings are sent to a human analyst, a SoundThinking employee, who reviews the recording and enters an assessment of what it contains (e.g. if it is gunfire, and how many rounds). If the analyst confirms the report, an alert is sent as a text message (I believe in an app they furnish) to staff in APD's dispatch center, called the Emergency Communications Center (ECC). The contract includes an SLA on this process of I think 1 or 2 minutes, but I was told that they routinely performed as well as 30 seconds. Some APD personnel, I think usually area commanders but it may have been all field division sergeants, also receive the alerts on their phones.
The ECC dispatches the call as a priority 2. P2 is high enough that a ShotSpotter report will "bump" most calls for service except for a caller on the line violent crime in progress. When the officers arrive at the reported location, they make a brief assessment and search the area for suspects or victims. If no suspects or victims are found, a Crime Scene Technician is dispatched (often later as they will wait for daylight) to search the area for evidence such as spent shell casings.
My recollection is that I was told they were able to find definitive evidence of actual shots fired in less than five percent of cases, but take that with a grain of salt as I do not believe it was ever put in writing (I don't think they're allowed to by their contract) and I could be remembering wrong. However, it's believable that the accuracy of the system is higher than that suggests, as Albuquerque has a lot of wide open spaces that are difficult to search thoroughly if the ShotSpotter location estimate is at all inaccurate.
I was told that, when the system was tested by firing blanks, it was not completely effective but that they were satisfied with how effective it was. I was never given a number and I think they had been very specifically prohibited from discussing the testing in detail when they coordinated it with SoundThinking.
One of the major criticisms of the ShotSpotter system in Albuquerque is that it results in a relatively large volume of P2 calls that delay police response to most other calls for service. During the worst of the understaffing, I was told that some officers in high-crime areas like the International District spent a large portion of their total shift following up on ShotSpotter activations while there were multiple P3 calls queued. This has probably improved as staffing levels have increased, but in my mind it is the greatest single concern about the system.
SoundThinking's evasiveness, refusal of independent research, and clear motive to sell their product creates an alarming possibility that they are deceiving police leadership and elected officials into overprioritizing ShotSpotter. It may be a waste of money, which is already a problem, but the much greater concern is that police departments are putting off responding to nonviolent crimes in progress to go to ShotSpotter reports instead, because they have been told by SoundThinking that the accuracy rate of the system is very high.