# Proximity sensor for car starting? **URL:** \ **Category:** Factual Questions\ **Created:** [July 22, 2007, 12:18pm UTC](https://boards.straightdope.com/t/proximity-sensor-for-car-starting/412741 "2007-07-22T12:18:20Z")\ **Posts on this page:** 12\ **Page:** 1
**Author:** ![Dog80](https://avatars.discourse-cdn.com/v4/letter/d/6bbea6/32.png) [@Dog80](https://boards.straightdope.com/u/Dog80)\ **Post date:** [July 22, 2007, 12:18pm UTC](https://boards.straightdope.com/t/proximity-sensor-for-car-starting/412741/1 "2007-07-22T12:18:20Z")
Many new cars have proximity sensors instead of keys for starting the engine. For example, what you get instead of a key is a credit card shaped remote control. As long as that card is somewhere inside the car, eg. in your pants pocket or inside the glove box, you press the START button on the car and the engine starts. If the card is not present, pushing the START button won’t do anything. My car (Citroen C4) has an ordinary key for starting the engine. I want to keep the key, but I was wondering if there is any aftermarket proximity sensor that I could use to cut-off something vital (such as the fuel pump power supply) for added security. So even if someone somehow gets my key, it will still be impossible to start the car without the proximity keycard. I intend to keep that card in a secret pocket in my pants 😃 ---
**Author:** ![Small\_British\_Shop\_Owner](https://avatars.discourse-cdn.com/v4/letter/s/e56c9b/32.png) [@Small\_British\_Shop\_Owner](https://boards.straightdope.com/u/Small_British_Shop_Owner)\ **Post date:** [July 22, 2007, 12:20pm UTC](https://boards.straightdope.com/t/proximity-sensor-for-car-starting/412741/2 "2007-07-22T12:20:16Z")
Why on earth would anyone steal a Citroen C4? There may be such a device around, but I would think very hard before messing with a modern car’s electrics, especially if it is still under warrenty. ---
**Author:** ![Myglaren](https://avatars.discourse-cdn.com/v4/letter/m/f1d935/32.png) [@Myglaren](https://boards.straightdope.com/u/Myglaren)\ **Post date:** [July 22, 2007, 12:35pm UTC](https://boards.straightdope.com/t/proximity-sensor-for-car-starting/412741/3 "2007-07-22T12:35:53Z")
Previous Xantias had a similar system that was built into the key. My current C5 hasn’t - there must be a reason for that. ---
**Author:** ![Uncommon\_Sense](https://avatars.discourse-cdn.com/v4/letter/u/f9ae1b/32.png) [@Uncommon\_Sense](https://boards.straightdope.com/u/Uncommon_Sense)\ **Post date:** [July 22, 2007, 12:51pm UTC](https://boards.straightdope.com/t/proximity-sensor-for-car-starting/412741/4 "2007-07-22T12:51:49Z")
[QUOTE=Dog80] Many new cars have proximity sensors instead of keys for starting the engine. For example, what you get instead of a key is a credit card shaped remote control. As long as that card is somewhere inside the car, eg. in your pants pocket or inside the glove box, you press the START button on the car and the engine starts. If the card is not present, pushing the START button won’t do anything. My car (Citroen C4) has an ordinary key for starting the engine. I want to keep the key, but I was wondering if there is any aftermarket proximity sensor that I could use to cut-off something vital (such as the fuel pump power supply) for added security. So even if someone somehow gets my key, it will still be impossible to start the car without the proximity keycard. I intend to keep that card in a secret pocket in my pants 😃 [/QUOTE] that could turn out to backfire when the wife says, “Honey, I think it’s TIME!!!”. Dammit, where the hell’s my card? 😃 ---
**Author:** ![AskNott](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/asknott/32/5790_2.png) [@AskNott](https://boards.straightdope.com/u/AskNott)\ **Post date:** [July 22, 2007, 1:05pm UTC](https://boards.straightdope.com/t/proximity-sensor-for-car-starting/412741/5 "2007-07-22T13:05:03Z")
[QUOTE=Small British Shop Owner] Why on earth would anyone steal a Citroen C4? … [/QUOTE] Some car thieves do it for the joy of doing something crazy. An old friend of mine, as a wild kid, stole a school bus. He drove around madly until it ran out of fuel. 🆒 I want to know where **Dog80** can find pants with secret pockets. ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [July 22, 2007, 1:07pm UTC](https://boards.straightdope.com/t/proximity-sensor-for-car-starting/412741/6 "2007-07-22T13:07:20Z")
Those systems are very, very complex. There is a whole series of antennas that are hooked to a separate computer to control the entry and starting of the car. I doubt you will find an aftermarket system. Even if you did, if the guy at the stereo shop can wire it up, a thief can disable it. ---
**Author:** ![Dog80](https://avatars.discourse-cdn.com/v4/letter/d/6bbea6/32.png) [@Dog80](https://boards.straightdope.com/u/Dog80)\ **Post date:** [July 22, 2007, 10:31pm UTC](https://boards.straightdope.com/t/proximity-sensor-for-car-starting/412741/7 "2007-07-22T22:31:55Z")
[QUOTE=Rick] Those systems are very, very complex. There is a whole series of antennas that are hooked to a separate computer to control the entry and starting of the car. I doubt you will find an aftermarket system. Even if you did, if the guy at the stereo shop can wire it up, a thief can disable it. [/QUOTE] I don’t want to convert my car to start without a key. I understand that this will be extremely difficult without major modifications. All I want is a simple switch that is closed whenever the keycard is in proximity. I could then connect that switch to something like the fuel pump or maybe the starter motor. If the keycard is in proximity, the switch is closed and I can start the car with the key, as usual. If no keycard in proximity the switch remains open and the car won’t start. ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [July 22, 2007, 11:35pm UTC](https://boards.straightdope.com/t/proximity-sensor-for-car-starting/412741/8 "2007-07-22T23:35:14Z")
[QUOTE=Dog80] I don’t want to convert my car to start without a key. I understand that this will be extremely difficult without major modifications. All I want is a simple switch that is closed whenever the keycard is in proximity. I could then connect that switch to something like the fuel pump or maybe the starter motor. If the keycard is in proximity, the switch is closed and I can start the car with the key, as usual. If no keycard in proximity the switch remains open and the car won’t start. [/QUOTE] OK assuming that you just want it to start the car. Silly asseds question that leap to mind. How are you going to lock the car if you leave the key in the ignition? :smack: If you answered via the remote, you had better check again, many of them will not lock / or arm the alarm if the key is in the ignition. :smack: ---
**Author:** ![Q.E.D](https://avatars.discourse-cdn.com/v4/letter/q/51bf81/32.png) [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)\ **Post date:** [July 23, 2007, 12:00am UTC](https://boards.straightdope.com/t/proximity-sensor-for-car-starting/412741/9 "2007-07-23T00:00:22Z")
[QUOTE=Rick] OK assuming that you just want it to start the car. Silly asseds question that leap to mind. How are you going to lock the car if you leave the key in the ignition? :smack: [/QUOTE] I don’t think you understand what he wants. Assuming I’m reading him correctly (and I’m sure I am), he wants a system which will let him use his keys as normal, but will not allow the car to start if the RFID card is not present. In other words, even if someone steals his keys, they will not be able to start the car unless they know to also steal the RFID card, too. He’s not going to leave the keys in the ignition. ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [July 23, 2007, 5:08am UTC](https://boards.straightdope.com/t/proximity-sensor-for-car-starting/412741/10 "2007-07-23T05:08:10Z")
OK, I can buy that, but according to [Citroen](http://www.citroen.co.uk/c4/) the c4 already comes with a chipped key/transponder with an engine immobilizer. I am fairly sure that these systems have been required in Europe for several years to combat auto theft. Color me confused. There are aftermarket immobilizer systems, but every one I have seen requires a “key” to be inserted into a switch. I have not seen any that work like the new keyless entry/keyless start systems. ---
**Author:** ![Dog80](https://avatars.discourse-cdn.com/v4/letter/d/6bbea6/32.png) [@Dog80](https://boards.straightdope.com/u/Dog80)\ **Post date:** [October 9, 2007, 1:52pm UTC](https://boards.straightdope.com/t/proximity-sensor-for-car-starting/412741/11 "2007-10-09T13:52:04Z")
I am resurrecting this old thread because I found what I was looking for. [http://www.helmetheadcyclegear.com/cgi-bin/eShop/index.cgi?pid=7290](http://www.helmetheadcyclegear.com/cgi-bin/eShop/index.cgi?pid=7290) Although it is intended for motorcycles, I don’t see why it couldn’t be used on a car. ---
**Author:** ![Tuckerfan](https://avatars.discourse-cdn.com/v4/letter/t/eada6e/32.png) [@Tuckerfan](https://boards.straightdope.com/u/Tuckerfan)\ **Post date:** [October 9, 2007, 3:55pm UTC](https://boards.straightdope.com/t/proximity-sensor-for-car-starting/412741/12 "2007-10-09T15:55:22Z")
[This](http://autospeed.com/A_107975/cms/article.html) appears to be similar and a _lot_ less expensive.