There are numerous watches on the market for running workouts, along with different apps, that will capture speed, time, and possibly heart rate. Many can also tell you different times to walk vs. running. I do not get more fancy than that with my current watch. I start it when I go and stop when done, sometimes looking at heart rate and time (for intervals and turn around times). For longer runs I also set it for a run/walk feature (anything over 1.5 hours I run 2 minutes and walk for 30 seconds).
Even though running is the lowest tech of all the tri sports, I know that there are some other tech features on the market. There are pods that will attach to a shoe and measure cadence and theoretically tell you if you are running on the ball of your foot or heal (and other running metrics that are supposed to help you run better). Clearly these are a bit beyond my expertise as a low tech triathlete who lives the enjoyable lifestyle without too much tech.