It would be nice if there was a way to research ( about half the game ) a personal radar that would be able to track aliens at say, 50 meters radius. I know in Xcom this device was available and I used it to track down that last hiding alien that just kept running away. The device would work better if your character has more Mind points, so perhaps a standard range of 20 squares + mind / 4 ? That means if you character has 60 mind ( that's quite a lot ) it would be able to track aliens at 40 squares away. Ofcourse, equipping and removing the tracking device costs ALL your TU's , so you won't have time to track, then shoot.
This will make available an extra 'type' of character : Someone with high Mind who tracks down aliens. Most seal teams have a team-member that specializes in tracking ennemies so this is not like an absurd thing to implement, it would only add to the tactical level of the game 
In 'Very Hard' level , the last thing you want to do is go through a huge map with 100 small rooms and try and find that 1 alien which hides in a closet somewhere on the 5th floor... With a tracking device, this is history. Ofcourse, you can only track the alien types that you have indeed researched. We all know it can take HOURS sometimes trying to find that last alien , I think a tracking device would be very welcome.
For me personally, i think its a good idea to have one such device = a field radar.
Just the implementations, is one i dun really like. I saw X-force (another x-com inspired game), where this device can be employed earli in game. They can even be thrown (like a grenade but do not bounce).
However, it is strictly technologically based, and not on minds. Throwing requires throwing skills. (like grenade)
And the range? Maybe within 5 -8 sqs radius.
Otherwise, we could also go with Xcom original scanner (a scanner on hand) which takes up TU each time u use......
Then again, these are features, which we can implement after the MORE urgent and pressing issues (like pathfinding) are resolved. :p
