Alright, that may be the wrong name for it but I am needing some type of circuit to detect when another sensor is near it... Like, when sensorA is within 5 feet of sensorB to activate a circuit on sensorA side...

Sorry if that sounds confusing... I need this for 2 different projects really. Would this fall under Radio Control or something else? Also, I need it so the sensors can't easily be activated. I want only sensorB to activate sensorA and nothing else can trigger it. Hope that makes sense... but to give you a better idea, one will be a vibrating collar for my wife's dog when it gets near my cat (stupid dog has killed her entire litter and is working on trying to get her now)

The other project is going to be a sensor on a keychain so my truck will know when I get close to it... within a few feet or something. I'll have several functions running off of it. I really will have it set so I can use the truck without the key.

 

Hmmm... Rf wouldn't require a clear path to the receiver, but would be kind of battery hungry on the transmitter end. For the truck, they already have key chain remote controls that will operate most anything in the car, even start it for you, but guessing you don't want to push a bunch of buttons, just walk up to it and go.

Vibrating collar for the dog, isn't that more of a 'reward', unless the vibrating is followed by an incredible electric shock. You need a physical barrier between the kittens and other animals, male cats will kill male kittens if given the opportunity, less competition for mates, insures their bloodline. Oh well, don't have to worry about who to dump kittens off on, least for another 4-6 months, until the next batch...
Surprised momma cat didn't rip the mutt to shreds. I had a female Siamese, later picked up a 7 month old Rottweiler mix. She use to beat the hell out of him for no reason. He was a big dog, would have had no trouble killing that cat. Only took him seconds to kill a opossum.

 

ha, well she did beat the hell out of her (Jack Russle.. small dog). But while she was away from the kittens, she got in there and got all of them but 1.

But ya, I have one of those remote starts and all but I really like the idea of getting in and going. One thing I do is leave my keys in my pocket and it's always irritating after work to get out or move around and strain to get them out lol. It'd also have a cool factor to it as well

And yes, the collar could have a shock to it but from what I hear, vibrating can be discomforting to the dog as well. I would have figured that out later lol

 

You could use an inexpensive 433MHz Tx/Rx pair for the transmission medium, the maximum range will probably be greater than necessary but by omitting the antennas the range will be reduced. A means of encoding and decoding the signal and preserving battery life should also be incorporated.

For the lowest component count and compact size, a small micro-controller is ideal, however, if you are not familiar with programming there are encoder/decoder chips available (is Holtek HT12 range still available?). For your truck, the battery operated keychain transmitter does not need to transmit continuously so could be triggered to transmit briefly every 5 seconds or so by a low power timer IC such as 7555.
The same principle would apply for the dog collar-mounted receiver.

 

Anyone have a diagram for something like this?

 

Depending on the range that you need you may be able to use an RFID system. The system can be setup so only a key tag (fob) that is programmed into the unit would activate the receiver (i.e. Keyless entry system).

Might be a little bulky for a dog collar though.

Using the keyless access system design, you could let the cat carry the key fob that would activate a solenoid on a pet door that would only allow the cat access to a specific area.

You can google "RFID pet door" to get an idea of whats already available.

 

Ya, I've sorted out the dog & cat situation but I am still wanting a system like this for my truck.. Something to activate a relay or circuit when I'm within like 4 feet of my truck