Detect Lies
This house rule allows users of Detect Lies to make their own rolls, which some players enjoy. This house rule also includes information on using lie detection equipment. If you consider Detect Lies to be a cinematic skill, this house rule renders it less so. (If you like this house rule, you might also be interested in my Interrogation house rule.)
Detect Lies
Per/Hard
Defaults: Perception-6, Body Language-4, or Psychology-4
This is the ability to determine if somebody is lying by observing and interpreting physiological changes and psychological mannerisms.
A successful Detect Lies roll means you noticed a tell that indicates the person either lied or told the truth. The potential liar, however, gets a chance to defend using Acting or Fast Talk (or an IQ-5 default). If the liar makes his roll by more than you made your Detect Lies roll, the GM will give you an answer that favors the liar--you misinterpret a tell or believe a false one. An unsuccessful Detect Lies roll means you do not pick up any tells or they’re inconsistent. A critical failure means that person is particularly hard for you to read for some reason and you don’t trust yourself to reliably interpret their tells for the rest of that encounter. A critical success on your part or a critical failure on their part indicates the revelation of additional and/or unexpected information. Because of this game mechanic, PCs can be allowed to make their own Detect Lies rolls. WARNING: Under this house rule, a career liar will often fool you.
Detecting lies with lie detection equipment requires having spent at least 1 character point on Electronic Operations (Medical) skill. Lie detection equipment becomes available at TL 6 and gives a bonus to Detect Lies skill equal to your margin of success with Electronic Operations (Medical) skill, up to a maximum of TL-5 or your relative skill level, whichever is less. The person lying can resist with Body Control by regulating the normally involuntary physiological changes that occur when they lie. This is a regular contest, Electronics Operations (Medical) vs. Body Control. (Option: a good Actor without Body Control skill may be able to get into character enough that they, for all intents and purposes, adopt a new personality that is consistent with their lie. This is very difficult and amounts to a -7 penalty to their Acting skill.) When using lie detection equipment, you may make one Detect Lies vs. liar roll for the entire session if you wish. I.e. you ask all your questions then go over the results of the polygraph later.
An attempt to Detect Lies accurately under any circumstances requires you to get a feel for the tells of a particular individual; this takes 25 minutes for a total stranger. Apply a reduced time penalty of -1 for every 5 minutes you fall short of the requisite time. For a first-time subject and no time you start at a -5 penalty. This means that, if possible, you should spend 25 minutes of quality time with a stranger before you use Detect Lies.
Modifiers: +1 for Sensitive or +3 for Empathy (p. B51), or -3 for Low Empathy (p. B142); +4 if your subject is Easy to Read (p. B134). If the subject is of a different species, the GM may assess a penalty - see Physiology Modifiers (p. B181). Up to a TL-5 bonus with lie detection equipment. Up to a -5 penalty due to reduced time. (The liar may also receive bonuses. If an Actor has time to prepare, give them a +5 bonus. If a Fast Talker is saying little more than “yes” and/or “no”, give them a +5.)
Example 1: with lie detection equipment
You have IQ 11, Detect Lies at 15, and Electronic Operation/TL9 (Medical) at 12; a con man, who has had ample to to prepare his story, has Acting at 17. Your Electronic Operation/TL9 (Medical) roll is a 9 (made by 3) and the con man’s Acting roll is a 13 (made by 4--not enough to overcome the -5 modifier); you win the regular contest for getting a lie detection equipment bonus of +1 (your relative skill level). After spending half an hour with the grifter hooked up to lie detection equipment, you roll against your Detect Lies+1. If you miss, the lie detection results are inconclusive; if you succeed, the con man (we’ll assume he lies) gets an Acting+5 roll. If he succeeds by more than you, then he appeared to be telling the truth; otherwise, he appeared to be lying. You get a +1 because of the lie detection equipment; he gets a +5 because he had time to get into character. It would be appropriate to make the number of lies caught dependent on how successful your roll was and/or how unsuccessful his roll was.
Example 2: without lie detection equipment
At TL5 you ask a working women in a saloon her age and want to know if she’s telling you the truth. You have Detect Lies skill at 12; she does not have Acting or Fast Talk skill. This is a contest of your Detect Lies-5 vs her IQ. You take full reduced-time penalties in a situation like this; she gets a +5 bonus to her IQ-5 default for this easy lie. After about of half hour of conversation and observation, you could ask again. (Some GMs will assess a penalty for a repeated attempt.) Indeed, it is difficult to know with certainty when you are being lied to by a stranger in a social situation.