Hello I hoping to get advice on what type of sensor to use for my project. Without going into too much detail I would basically like a sensor that can detect when a particular object is close by. I was thinking some kind of rfid with a tag imbedded in the object but I need multiple sensors for the project and the price tag looked too high to make it feasible for my budget. I could use a simple infared detector but I would really like to make it so that a specific object is needed and the sensor can not be tricked by just any object moving in front of it. I also looked into hall effect or magnet sensors which I purchased and tested but they did not seem reliable or practical for my purpose since I could embed a magnet in my object but not close enough to the edge to effectively trip the sensor. I am hoping to use between 10 and 20 sensors in the project and they all will be detecting the same object or possibly two different objects if I can.
How many types of objects you are using ??? RFID is best option here but its a costly one and you have to attach RFID tag with every object.
So, you should find a way to differentiate objects, as you said you are using two types of objects then you can differentiate on the basis of their height may be and can use infrared or ultrasonic sensor HC-SR04.
Levister2121:
Without going into too much detail I would basically like a sensor that can detect when a particular object is close by.
When more detail you provide, better answers you can expect.
As I said without too much detail as in hopefully enough without rambling too much. I think I outlined the parameters pretty well but I am happy to answer any questions you have. I am not familiar with all the different sensors out there and am hoping people will give me suggestions that I can look into and rule out until I find the right one.
Levister2121:
As I said without too much detail as in hopefully enough without rambling too much. I think I outlined the parameters pretty well but I am happy to answer any questions you have. I am not familiar with all the different sensors out there and am hoping people will give me suggestions that I can look into and rule out until I find the right one.
Not really - what is close?? 0.006 inches?? 6 inches?? 6 ft?? 60 ft?? 600 yards??
All are to some "close" and to others not so close
Size and type of object is another question - a book or a truck??
As has already been said, the size, nature and distance are all significant, so you need to tell us more.
However I created some powerpoint slides for a course a while back that you may find helpful so here is a link
http://www.skillbank.co.uk/de/year3.htm
For "newer" sensors you might consider using a webcam and optical recognition.
Sense a particular object.
I have never seen a particular object sensor. Perhaps the object has other parameters that other sensors can detect.
Thank you very much for the link I will look into it later today!
There are lots of different sensors that can detect proximity of an object - IR based, ultrasound based, magnetic based, touch based, etc. That's one thing. Which is suitable depends on the objects in question and the distance required for closeness.
Then there are sensors that can identify an object. RFID is one, but other options include bar code readers, colour detectors, an array of hall or reed switches that trigger based on where the magnets are, etc. Again what works depends on the object in question, but also on the number of individual objects you want to identify. These sensors normally also require proximity, how close it has to be varies.
Without too much detail you will obviously not get too much of an answer. 
Put a radio in the particular object that is not covered with a Faraday Cage. Receiver will get strongest signal when pointing right at the source. 2 readers could triangulate, just how many times a second is hard to be sure.
Can it emit high frequency sound?
Can it be charged with static? Arduino can detect electric fields using capacity with field coupling.