This mod adds two blocks.
The first block emits a redstone signal while players are near; the other block emits a redstone signal while mobs are near.
The detection range of either block can be set to a 2-, 4-, 8-, or 16- block spherical radius; this range can by cycled by activating the blocks.
The mob detector can also be set to only detect one type of entity. This can be done by using a slimeball on an entity (either shift-right-clicking the mob or attacking it with the slimeball) to obtain an Imprinted Slimeball, then using the imprint on the mob detector. A filtered mob detector can be reset to detect all entities by using a regular slimeball on it, or breaking the block.
The blocks check for entities at a default rate of once every 10 ticks; this can be changed in the server config.
See images for recipes