Regularly thought speak has a range of 200feet. The Animorph does not need to see or even know where the recipient of their message is in order to send and have it heard. Messages sent over the 200ft range are often distorted, incomplete or not received at all. Within the range nothing will block a message from getting to its intended recipient.
Thought speak works almost identical to telepathy. There is no confirmation of a message being received. Messages ‘sound’ like those sending them and can be words, sounds, images or sometimes even feelings and sensations.
Thought Speak is a universal language and can be understood by anyone who hears it regardless of the known languages of those speaking. However only certain alien races and those in morph can send thought speak messages—an animorph in their base form can hear thought speak but not send it (unless they are an andalite or a yeerk who can use thought speak in their base forms). A certain level of sentience and a spoken language are required to understand thought speak. For example an Animorph could send a thought speak message to a squirrel but the squirrel will not understand what is said, only that it ‘hears’ something.
It is impossible to tell where thought speak is coming from. There are multiple ways to use thought speak, like settings. Default is one-on-one and any other settings must be announced. Settings can be groups of people, anyone in range, or anyone who meets certain specifications. These specifications can be quite varied, from ‘everyone who knows the speaker’ to ‘everyone in a blue shirt’.
A strong connection with someone does increase the effective range of thought speak. This usually applies to families and romantic partners.