There is a free service on the web called IMvisible witch can detect anyone with 100% accurate. Here you can find it
www.imvisible.info
Yes.
You should try http://www.pitit.ro
The point is that they do not want to be detected, you can always message them and see if they answer.
If they are appearing invisible on MSN/Hotmail messenger, there is no way of finding out. There are no programs to allow you to see if they are appearing online, Microsoft made this a privacy setting, so people who do not want to talk, but want to be logged in can do so.
They are invisible.
Spectrometer
No. There are not machines that can detect motion sensors. You may be able to detect the sensor rays through special lighting, but the beams are normally invisible.
yes
There are some useful programmes to check invisble status on hotmail ...
A drug test or a Urine test can detect just about anything that is in your system, whether it be legal or illegal. A drug test can detect whether or not you are taking birth control.
There are a number of softwares and programs that are used to detect the type of the motherboard. The CPU-Z software is the most commonly used software fr this purpose.
No. Are there undetectable walls in outer space? Possibly. We can't detect them.
Different devices are used to detect different frequency ranges of electromagnetic waves. You simply can't use the same device to detect x-rays, than you would use to detect radio waves, for example.