Sensor Device

Yes, there is. You are in luck.

so i can get it from market now??i wan know about the size of device and how to detect the missing object?thanks

Yes but you've got to find it first.

An RFID tag and a directional finder perhaps?

Cheap RFID tags and a corresponding reader work well for short range sensing. More expensive (but longer range) miniaturised radio transmitter/receivers work well also, while much more expensive GPS locater tags work at great distances. Low level radiation tags will work but I think an accurate locater is too expensive.

If it were me I would go with RFID tag technology (try a Google search), there are plenty of products on the market now days and the cost of both the tags and portable locator is fairly low.

Alternatively, just ask the wife where you left the objects.

thx in advance.so the size of sensor device could be very small like a mobile phone? and could we detect the object in the distance of 2-4 meters?

Yes to both questions. Try an internet search of RFID for existing products that will give you a good idea of what is commercially available right now.

There is also plenty of information and parts or custom RFID tags and designs available if you want to build your own products.