A safety housing based implant/medicament injecting system (100/200/300/400) comprising: a needle assembly (102/202/302/402) including implant/medicament for injection and an injecting needle/cannula (112/213/312/412) at its distal front end; a housing (101/201a-201b/301/401a-401b) with a front opening for the said needle assembly (102/202/302/402); said needle assembly (102/202/302/402) with said injecting needle/cannula (112/213/312/412) in said housing (101/201a-201b/301/401a-401b) maintained under usual bias in said housing (101/201a-201b/301/401a-401b); a plunger means (105/204-207/305/405) having a plunger rod (114/204/314/414) concentrically disposed with respect to said housing and said needle assembly, said plunger means (105/204-207/305/405) effects under its forward motion an initial exposure of said injecting needle/cannula (112/213/312/412) from said housing (101/201a-201b/301/401a-401b) at its distal front and followed by injecting out of the implant/medicament through said needle/cannula (112/213/312/412); said plunger means (105/204-207/305/405), said housing (101/201a-201b/301/401a-401b) and said needle assembly (102/202/302/402) having releasable seal means (106/206/318/404) enabling the plunger means (105/204-207/305/405) under an initial injecting plunger forward motion to couple only with said needle assembly ensuring co-movement of the needle assembly, the plunger means and the plunger rod to effect said initial exposure of the needle/cannula until a first engagement means (115/211-210/315/415) engaging the needle assembly with the housing when the needle/cannula is completely ejected through the front opening and thereby arresting any forward or backward motion of the needle assembly in the ejected state of the cannula for injection and thereafter opening of the releasable seal means by a seal releasing means (120-122/206/306/406), disengages coupling between the needle assembly and the plunger means and enables independent forward movement of the plunger means with respect to the needle assembly inside the housing for continuing injecting plunger forward motion of the plunger means which facilitates the plunger rod to enter the needle assembly for said injecting out the implant/medicament through the exposed needle/cannula; a cooperative first disengagement means(124/215/305-front-end/405-outer-body) for disengaging said first engagement means housing connection to said needle assembly post injecting of the medicament/implant enabling retraction of the used needle/cannula under its said usual bias into the housing and locked therein with respect to the housing by a second engagement means (107/211-212/307/407) to avoid any future use/accidental exposure of the used needle /cannula. a needle assembly (102/202/302/402) including implant/medicament for injection and an injecting needle/cannula (112/213/312/412) at its distal front end; a housing (101/201a-201b/301/401a-401b) with a front opening for the said needle assembly (102/202/302/402); said needle assembly (102/202/302/402) with said injecting needle/cannula (112/213/312/412) in said housing (101/201a-201b/301/401a-401b) maintained under usual bias in said housing (101/201a-201b/301/401a-401b); a plunger means (105/204-207/305/405) having a plunger rod (114/204/314/414) concentrically disposed with respect to said housing and said needle assembly, said plunger means (105/204-207/305/405) effects under its forward motion an initial exposure of said injecting needle/cannula (112/213/312/412) from said housing (101/201a-201b/301/401a-401b) at its distal front and followed by injecting out of the implant/medicament through said needle/cannula (112/213/312/412); said plunger means (105/204-207/305/405), said housing (101/201a-201b/301/401a-401b) and said needle assembly (102/202/302/402) having releasable seal means (106/206/318/404) enabling the plunger means (105/204-207/305/405) under an initial injecting plunger forward motion to couple only with said needle assembly ensuring co-movement of the needle assembly, the plunger means and the plunger rod to effect said initial exposure of the needle/cannula until a first engagement means (115/211-210/315/415) engaging the needle assembly with the housing when the needle/cannula is completely ejected through the front opening and thereby arresting any forward or backward motion of the needle assembly in the ejected state of the cannula for injection and thereafter opening of the releasable seal means by a seal releasing means (120-122/206/306/406), disengages coupling between the needle assembly and the plunger means and enables independent forward movement of the plunger means with respect to the needle assembly inside the housing for continuing injecting plunger forward motion of the plunger means which facilitates the plunger rod to enter the needle assembly for said injecting out the implant/medicament through the exposed needle/cannula; a cooperative first disengagement means(124/215/305-front-end/405-outer-body) for disengaging said first engagement means housing connection to said needle assembly post injecting of the medicament/implant enabling retraction of the used needle/cannula under its said usual bias into the housing and locked therein with respect to the housing by a second engagement means (107/211-212/307/407) to avoid any future use/accidental exposure of the used needle /cannula.