This little portable mine is a sleeping beauty that utilizes a weighted base and ultrasonics to wake up when anything moves into its 1-meter detection radius and greet it with a 6-meters radius explosion. Exceedingly useful for trapping various choke points such as corridors in base defense missions and UFO doors.
Earning experience the hard way
Unlike other explosives, the Proximity Grenade does not give firing accuracy experience points for hits to the person throwing it (although this will give you throwing experience). Instead, it gives firing XPs to the person, or more optimistically, alien, who triggers it to explode.
Unfortunately, the accompanying pain and death make it a dubious choice for earning experience, especially early in the game (when you don't have the armor to go near one). For more on experience points, see here. You can use UFO Extender to give the person throwing it the experience.
- I made the finding that Prox Grenades goofily give experience to the person that made it explode. But it's occurred to me that I triggered the Prox with soldiers in FS armor, and there may be different outcomes if an alien triggers it and/or the unit that triggers it dies. If anyone wants to look into this, have at it. I don't have the time ATM. - MikeTheRed
Among the aliens, Mutons can survive the explosion handily. Keep a few snipers around so they won't live long enough to benefit from the experience.
Mining UFO doors
One of the most popular uses of the Proximity Grenade is to place one just outside a UFO's outer door. Aliens emerging from the craft will take a face full of HE, commonly killing weaker species such as Sectoids, Floaters, and Snakemen, and weakening most others.
The grenade must be thrown one space away from the door, in the location marked "G" in the diagram at right. If the grenade is placed immediately in front of the door, it will detonate when the alien is still on the other side of the door, and the alien will take no damage.
This technique is particularly effective around Turn 20 of combat. Aliens have a known habit of emerging from their UFO right around Turn 20. Some may remain in the craft, but several can be killed in the space of a few turns.
It is also recommended to have several troops facing the UFO door (from a distance), to kill any aliens which might survive the blast. This technique is detailed in depth at Reaction Training.
This technique has a few drawbacks: aliens killed by a Proximity Grenade will not earn your troops combat experience, and the grenade will destroy most nearby objects on the ground. If you have already killed one alien this way, its corpse and equipment will be lying outside the door, which will be destroyed by a subsequent explosion.
This problem can be addressed by posting a "looter" just around the corner from the door (see the picture to the right for placement). After a grenade detonates, the looter should pick up one or more valuable items, retreat around the corner again, and another soldier can throw a new grenade, if desired. Ideally, the looter should have high TUs (60+), and you should not try to pick up everything unless you are certain the looter has sufficient TUs to get back to safety. Many looters have been lost due to lack of speed and excess of greed.
Another possibility is to throw the proximity grenade just inside the door to the UFO. When the grenade is set off, the explosion is confined to the inside since HE damage cannot propagate through the tough hull. This means your soldiers can stand extremely close to the door and not worry about being hurt (from the grenade, anyway). When used in conjunction with a Motion Scanner, you can determine if aliens are close to the mine and decide whether to deliberately set off the grenade by walking up to the door.
Proceed with caution
Proximity mines can often cause "friendly fire" casualties. It is easy to forget a grenade placed several turns ago and to stumble into it, killing your own troops. An undetonated grenade can also cause the "phantom grenade" bug described below.
It is therefore best if you deliberately destroy undetonated grenades. This can be accomplished easily by throwing a standard armed grenade on top of one. It may be necessary to destroy Proximity Grenades left outside a UFO door as well, if no alien emerges after many turns.
Proximity Grenades can also be removed through the use of Flying Suits. A grenade will not detonate when a unit moves into its detection radius vertically -- so a soldier in a Flying Suit can safely approach the grenade while flying, drop down on top of it, and pick it up. The grenade will remain armed, but it will not detonate unless it is dropped and then triggered by movement.
When a primed Proximity Grenade accidentally lands in an adjacent square to your soldier when doing Grenade Relay that soldier can safely move away from it - it won't trigger.
In some versions of the game, a bug causes armed-but-undetonated Proximity Grenades to transfer their properties to a different item in the next mission, which may then explode unexpectedly. If an explosion goes off just as your first soldier steps out of the transport, you have fallen victim to this bug.
The easiest way to fix this is to save the game at the beginning of Turn 1, before any soldiers move. If something explodes, reload your file; the phantom grenade will be deactivated.
This is due to a different bug, common to the computer versions of the game, in that all Proximity Grenades lose their "armed" status when restoring from a save. If the player so chooses, this can be exploited to disarm unwanted mines. In the Playstation version Proximity Grenades do not have this bug.
- Proximity grenades are worth considering as an alternative to regular grenades when attacking aliens, especially in confined spaces such as X-COM and alien base corridors, where they are harder to avoid. Thrown at the feet of aliens, they function as if they had a timer setting somewhere between 0 and 1 -- going off after the end of your turn but as the aliens move. They are significantly more powerful than regular grenades making them especially useful against armoured aliens and those with high health.
- On higher skill levels, many aliens can survive the blast of a proximity grenade. Mutons always shrug them off, some Snakemen and even the occasional Floater will survive. But even when a proximity grenade doesn't kill, they are still useful to soften up targets and -- perhaps more importantly -- acting as burglar alarms. When you see a prox grenade go off, it will alert you to an alien in the area.
- PGs can safely be picked up by entering their square vertically (e.g. with flying suit).
- Just like all other live grenades in the game, it's safe to pick up an armed proximity grenade -- if it is already in your square.
- PGs detect movement into, but not out of, the eight surrounding squares, meaning you can walk away from a mis-throw.
- If all else fails, and you are trapped with nowhere to move and no way to defuse the mine: just stay still. Don't move and wait until the bomb squad arrives (i.e., wait until the mission ends). Additionally, keep other soldiers away from the unexploded mine.
- PGs can be destroyed by explosives. A standard grenade works quite well.
- With proximity grenades it's important to be aware of the BUG in the game - proximity grenades seem to disarm themselves if you resume a saved game. Makes load/save tactics impossible in a game where you are relying on proximity grenades.
- Kasey Chang's X-COM walkthrough mentions that you can pin aliens by throwing a proximity grenade on either side of it. This is bunk -- the game's AI is oblivious to proximity grenades, meaning aliens will do nothing to avoid them. Additionally, the first proximity grenade will destroy the second one.
- Never use proximity grenades on Zombies -- this will just spawn a enemy Chryssalid during the aliens' turn, which can immediately attack you.