But as such, there are conditions to consider where it shouldn't work as currently implemented:
1. It may not be able to magically differentiate between enemy mechs and friendly (unless the assumption is that friendly mechs are networked somehow as with Identify Friend or Foe (IFF) technology (which exists today).
2. If proximate enemy mechs are standing still - no return.
3. Assuming the sensor must
A. operate by keeping one foot in contact with the ground to pick up vibrations, and
B. both feet on the ground to calculate two dimensional location,
mechs should only get ping like accurate locational updates when BOTH FEET are in contact with the ground making it seem somewhat more like sonar ping returns when you are walking even though it is a passive sensor. When you are running with one or both feet off the ground it would freeze incoming reception. If only one leg is on the ground, (or if one leg is missing) then you cease to get seismic location updates. Sucks for you.
If you want to add an active RF type sensor module to either ping or rotationally or otherwise scan for big fusion reactor powered metal machines (like BAP should for instance supposedly being able to pick up shutdown mechs within 200m though I haven't seen it work), this might be cool, though active sensors do give up your ability to keep the location hidden.
Alternately, this provides an opportunity to implement either a consumable sensor you can plant on the map and transmit seismic or BAP like returns to your team, or perhaps a ballistic (similar to missile NARC or energy TAG hardpoint occupying) dispenser of such a sensor. Maybe allow opposing team to destroy them when discovered even.
Finally, seismic should share it's returns with the team - perhaps as a function as part of the command module suite of functions, or otherwise. It's unusual that you can see the network of friendly mechs on your map and not also share seismic data with your team.