Yes. However, the right to make this request may not be abused by a team, and only detailed information about his/her own team may be provided. For the opponent team the only information that will be provided will be whether or not the players are correctly positioned. No information will be given about which players are front or back row players. Rule 5.1.2.2

The use of such devices is allowed.

Only the game captain is authorized to speak to the referees to request explanations. The coach is not authorized to do so. Rules 5.1.2, 5.2.3.4, 21.1, 21.2, 21.3

The coach, and only the coach, has the right to walk in the free zone during the match between the extension of the attack line and the warm-up area without disturbing the game and the work of the line judge/2nd referee.

The referees may need to remind him/her regarding this requirement. If the coach consistently ignores the referees’ reminders to be between those limits, he/she may be warned. Rule 5.2.3.4

No. These persons have the right to do itsolely during the official warming up before the match. Only the players have the right to warm up in the free zone between sets. During the intervals the coaches may give instructions to the players. The referees should instruct the coach or assistant coach in a polite way to return to the team’s bench. Rules 4.2.4, 5.3.1

The situation may be different depending on the position of the person and the procedure of the warming up session.
In case of common official warming-up at the net the general principle is, that the warm-up can be practised solely in the team’s OWN playing area. However, it is allowed for the officials appearing on the team list to be close to the posts in order to avoid that a ball dropping down from the net can create a dangerous situation for the players. The person in the opponent’s playing area has no right to disturb the opponent’s warming up. But to stay far from the net (i.e. behind the end line of the opponent) and collect the balls or actively participate in the warming up is forbidden.

The referees should instruct the person in a polite way to leave the opponent’s free zone and return to his/her own half of playing area or to be close to the post. 

In case of separate official warming up the entire playing area may be used by the team actually warming with the balls at the net. The other team can use the free zone behind its own court, without disturbing the team at the net.

No, this is an abuse of the rule which permits sharing the net during the warm up. The coaches and any assisting players must be politely but firmly instructed to conduct this activity (with accompanying materials) from their own side of the net to avoid conflict with opponents or potential injuries. However, it is allowed for the officials appearing on the team list to be close to the posts in order to avoid that a ball dropping down from the net can create a dangerous situation for the players. 

For FIVB, World and Official competitions for Seniors these devices must be of the same colour as the corresponding part of the uniform, but the black, white and neutral colours are accepted. However if teams are using compression pads, they must be uniform in colour /design for all the players. During FIVB World and Official Competitions the referees must control this and inform of any violation to the FIVB Technical Delegate who is the person entitled to take the final decision on this matter. However, for competitions not listed above, the rule says nothing about the uniformity of the colour of the compression pads used by multiple players. Rule 4.5.3. FIVB Event Regulations