According to Mr. Clark's research, if you use a 1 to 2 MW (megawatt) laser and convert it into a 30-45 meter telescope and go into outer space, you can completely let sunlight and light from distant space Can produce separate beacons.
A civilization exists on a planetary system adjacent to the solar system, for example, TRAPPIST-1 located at about 40 light-years from the solar system, if you observe the direction of the earth on that side, you can recognize this lighthouse It could be. If you make the beacon illuminate regularly, you should be able to send a message like the Morse code.
Then, if it is possible to make such a beacon with the current technology, the answer is yes. For example, Chile in South America is Southern EuropeAstronomical Observatory(ESO) is building a super-large telescope (E-ELT) with a length of 39 m and the US-mounted YAL-1 missile interceptor laser has a megawatt power.
However, even if the laser that becomes this beacon weakens away from the earth, if it looks directly, there is the possibility that the eyes of the creature may be destroyed. Also, if you try to drag the ground out of a space ship with a camera, you can destroy the camera with its laser light. For this reason, Mr. Clark suggests that setting the laser beacon on the back of the moon, that is the part of the outer space, is the safest in terms of practical but minus.
But if we had a civilization on the planet to which we sent the beacon, thinking about the same thing with us and emitting a laser to the ground? Until now, we have never been able to capture signals from other planets than from Earth. To catch it, you need a large telescope with a diameter of 1 m or more and you have to sort your goal toward the planet.
In this respect, Mr. Clark will be able to know the possibility of life from the atmospheric components of the extraplanets if the development of infrared imaging technology to investigate the extra-solar planet's atmosphere is advanced, and among us we think. Such signals can also be detected.
It would not be impossible to invite your opponent in our house and be a kind of dish, as long as we find the light from the other entrance. If he does not try to annihilate us like the Martian of Marte Attack!