BSTL900 series 4 way kit contains:

4 x 801 handset (Dimensions: H 212mm x W 85mm x D 55mm)
1 x SPA1 surface mount entrance panel (Dimensions: H 190mm x W 102mm x D 38mm)
1 x Mod61 speech amplifier
1 x 212 12V AC fused transformer
1 x 203 surface mount electric release (suitable for surface mount night-latch style lock – for flush mount option see related products)