Make it a habit to have somebody check on you periodically to make sure that you are some place expected at a given time. The moment that you are not at some place where you are supposed to be, and you cannot communicate your whereabouts, it must be presumed that you are arrested.
The first few hours of your arrest are very crucial as during this time we can usually obtain information as to the probable law enforcement units which picked you up, and where you are currently detained, and there are still some friendly law enforcers who would be willing to provide useful information. If you are located during these first few hours, we can determine the responsible unit. Most of those who disappeared without trace were not tracked as to the responsible law enforcement unit within the first 24 hours of their apprehension.
Your relatives should, as soon as possible, contact a lawyer. If they cannot, at least they should write a letter-request to the judge, or the executive judge in multiple sala courts, of the Regional Trial Court having jurisdiction over the area where the arrest could have possibly happened, inquiring if there has been a written notification of your arrest, including your aliases. The law does not require the judge to respond to this letter; the implementing rules and regulations may consider this information as classified and the judge may be proscribed to divulge the facts without clearance from the Court of Appeals. Still, the received copy of the letter may be evidence to use for a case of non-notification of the judge. (Note that while the law requires that the Commission on Human Rights be informed as well, there is no penalty in the law for failure to inform the CHR.)
If the law enforcement unit is identified, your relatives or lawyer should demand a certification of the relevant entries of the official logbook pertaining to your arrest. Failure to provide such certification is punishable by imprisonment of 10 years.